YOU’VE made it. You’ve either climbed the corporate ladder, toppled the previous head of state or are now straightening your shirt having done the victory dance that accompanies those lotto numbers flashing on the television screen.

While the world has become your oyster and a plethora of life choices now present themselves, the decision regarding your main means of transport has now essentially boiled down to this: to drive, or be driven?

You could keep a low profile, both literally and metaphorically, as you sprawl out in the cavernous rear of Audi’s understated and elegantly crafted, stretched A8L 4,2 TDI. Or you could just as likely be drawn to the presence and theatre of the technological treasure trove that is the (marginally) smaller Mercedes-Benz S500 BlueEfficiency.

But before the lustful lunge towards the gathered grand sedans is even in mid-flight, we’re well aware that some readers will wonder exactly why these two cars are sharing the page.

True, it would be like comparing apples with pears. But there’s a question pertaining to both: how do you approach the common goal of serving up the last word in ultra-luxurious motoring?

Even so, the appraisal of both cars in their own rights, along with an exchange here and there, still makes for a fascinating poser.

Exteriors

If there’s a more subtly styled mode of statesmanlike transport than the A8L, we’ve yet to encounter it. A cursory glance from a distance would more often than not have the Audi confused with its smaller brother, the A6.

The A8’s attire is taut, neatly creased and more Bauhaus than bling: a combination that allows the car to wear its extended wheelbase very comfortably. Only by venturing closer and pacing out the 5,2 metres from nose to tail, and then taking in the shoulders that measure nearly two metres, do you appreciate just how much pavement the A8 occupies. Some may bemoan the lack of artfulness about the A8’s styling, but there is something inherently cool and clandestine about a stretched luxury car that barely registers on the radar; indeed, those who want to travel incognito will warm to it immediately. Only the new LED indicators with their Knight Rider-esque swooping illumination and the jewel-like full-LED Matrix headlamps go some way to piercing the stealth sedan’s cloak of invisibility.

By contrast, the S-Class gets noticed wherever it goes. Although it sits on a standard wheelbase, there’s only a 153 mm difference in overall length separating it from the A8. Where the Audi’s sheet metal is tightly drawn about its frame, the S-Class’s bodywork billows and tapers in a manner that accentuates its already considerable dimensions. Although Mercedes’ design language has taken a noticeably more adventurous tack of late that’s ushered in a riot of character lines and huge, intricate headlamps on smaller offerings, things have been toned down a touch on the S-Class. There’s sufficient head-turning value to the illuminated drop lines in the headlamps and the boat-tail treatment of the rear, for sure. But while it manages to be imposing, it nimbly treads a fine line that’s more ministerial than crass, capable of attracting attention and garnering admiration in equal measure.

Interiors

Climbing inside, the aesthetic divergence between the two cars is not so much echoed as amplified... It’s all about space, simplicity and solidity in the A8. Like most members of the Audi stable, the Ingolstadt-based firm’s flagship has always been adorned with a cabin that is beautifully crafted and materially peerless to the extent that many of its rivals’ interiors
are made to look low-rent by comparison.

There’s that clean, Bauhaus air to the cabin’s design, and an impression that the interior’s function determines its form. As such, that exterior aesthetic tautness is echoed within. The painstaking manner in which the wood veneers meet brushed metal finishes and grand leather is astounding, and there are no superfluous details.

This model’s 3 122 mm wheelbase, which is 130 mm longer than that of the standard car, contributes to a business class-like 870 mm of rear legroom. The impression of spaciousness is further enhanced by the reclined seatbacks and light-coloured headlining, although the attitude of the former, with its flat, firm cushion, doesn’t lend itself particularly well to any posture other than decidedly laid back.

Rear occupants are confronted by a brace of screens controlled by a scaled-down version of Audi’s MMI housed in the centre armrest that allows them to access audiovisual media, adjust their individual climate settings and, in keeping with the business-class motif, a view of the sat-nav map.

Although bristling with technology, the A8’s facia layout feels a bit dated. Yes, it’s slick, but the functional simplicity is eroded by a number of similarly sized buttons and knobs, some of which require a stretch of an arm to operate. And, while there’s no denying the build quality and the acreage of cabin space, some will find the interior somewhat austere.

The same cannot be said of the S-Class. When you consider the constituent parts – the brace of huge TFT instrument screens, cross-stitched leather trim, swathes of LED ambient lighting and brushed chrome-effect garnishes – there’s the potential for an overindulgence of sensory stimuli. However, the result is anything but.

There’s a genuine sense of occasion to the W222’s interior – from the bows of wood and leather gracing the gently billowing facia, to the metallic-feel of the switchgear and spherical ventilation pods up front, to the almost pillow-like rear seats – it’s executed in a manner that’s classically handsome and cossetting.

The S-Class’s approach to ancillary controls is a double-edged sword. While burying much of the functionality within the Comand system has eliminated facia clutter, mining into the configurations does require a fair bit of navigation and dial twiddling. Given that Mercedes-Benz claims that the average age of an S-Class buyer is in excess of 60 years, it’s moot whether the systematic approach of the A8 interface, albeit through a bewildering array of buttons, could suit owners better.

There’s also substance to the Benz’s style. The standard of the material and build quality have been elevated to the extent that the S-Class’s cabin can legitimately be mentioned in the same breath as those of some Bentleys and Rolls-Royces.

The S-Class’s wheelbase is 77 mm shorter than that of the A8, and by virtue of the enlarged front seatbacks, equipped as they are with devices that provide active bolstering and massage-producing functionality, it’s not a surprise that the Benz affords 110 mm less kneeroom than the Audi. Its plush, electrically adjustable rear seats have a wide range of configuration but, as is the case with the A8, they’re optional.

In both cars, you’re cocooned in cabins that are well insulated from engine and exterior noises. Tyre roar is perceptible on rougher surfaces, but relative to most other passenger (lesser) vehicles, hardly so. Trim and leather creaks are noticeable over bumps, but that’s because everything else is so hushed. If we had to pick one cabin over the other for best noise suppression, the Benz’s double-glazing would give it the edge.

Performance

The general consensus among the CAR team is that these grand sedans showcase the most impressive engines in the manufacturers’ large-engine lineups.

Channelling a tarmac-rippling 850 N.m of torque to all four wheels, the 4,2-litre V8 turbodiesel gives the A8 a startling turn of pace out of the blocks and it reached the 100 km/h mark from standstill in just 5,33 seconds. Even when town driving is the order of the day, the diesel remains deeply impressive – flexible enough to deal with both cut-and-thrust traffic and stretches of serene cruises with aplomb. The refined V8 turbodiesel merely utters a distant rumble when the throttle pedal is applied.

Refined though it may be, it still can’t quite hold a candle to the demeanour of the S-Class’s whisper-quiet 4,7-litre, twin-turbo V8. Although 150 N.m down on torque, the Benz’s engine hits back with 335 kW versus the Audi’s 283 kW, lending it astonishing mid-to-upper-range grunt reflected in overtaking acceleration times that eclipsed those of the A8. In fact, its demure soundtrack gives little hint to the speed that the S carries. The petrol V8 is delightfully flexible and performs both powerhouse and pottering roles to a tee.

As sterling as its powerplant may be, the S-Class’s transmission occasionally disappoints. Although smooth and composed on the open road, it succumbs to a spot of lurch under moderate acceleration from crawling speeds. The A8’s ‘box has no such issues: its silken in sedate driving and sharp under hard-driving scenarios.

Dynamics

The A8 must also be commended for its ride quality that, thanks to revisions to its adaptive-damping module, represents a palpable improvement over that of the previous model. It runs the S-Class surprisingly close, although the Mercedes’s overall composure over broken surfaces is noticeably better. As with all air-suspended cars, both waft along gracefully most of the time, only being caught out by sharp road imperfections that occasionally thud through to the cabin.

Under chauffeuring duties, the dynamic limits of these cars will seldom be explored owing to the fact that doing so will leave their well-heeled rear occupants flailing in a maelstrom of pages from the Financial Times and spilled espresso.

But, should owners opt to drive the vehicles and be in a bit of a hurry, they’ll find the A8 is best savoured as a passenger. Although the all-wheel-drive system does a great job of channelling the diesel’s grunt to the road and the sports differential helps tuck the nose in on sweeping bends, the steering is trifling and uncommunicative. The adaptive-drivetrain system, although fun to play with, gets flummoxed by sudden changes in throttle inputs and steering attitudes when in its automatic setting (it’s never quite sure when to stiffen the springs or take it easy).

Although prone to understeer when really pressing on, the S-Class surprises with agility unbecoming of a car its size. The steering is slightly artificial in feel, but responds with more directness, and the body control is far more fluid and predictable.

Test Summary

There’s a good deal to be said for the Audi’s understated-yet-accomplished approach. Going the long-wheelbase, diesel-powered route with the A8 doesn’t impact on the serenity of proceedings. It means there’ll be more time for occupants to enjoy creature comforts while surveying scenery that’s more appealing than a fuel station’s forecourt. But the lack of driver involvement means that the A8 is best sampled in its aft quarters.

If ultimate rear sprawling space isn’t a priority, the Mercedes makes a very strong case for itself as the most complete all-rounder in the grand saloon realm (and besides, an S500L is also available that addresses interior-size concerns). Where the A8 makes you feel important, the S-Class’s sense of occasion and refinement makes you feel special. The fact that it’s surprisingly rewarding to pilot also extends its appeal.

The nature of this test means that the final arbiter of choice is entirely subjective, which is rather frustrating when confronted with two accomplished products. But, few will argue that it is a wonderful conundrum to contemplate.

Road Test Scores:

Audi A8L 4,2 TDI - 82/100
Mercedes-Benz S500 BE - 86/100