Audi A6 vs Lexus GS vs Mercedes-Benz E-Class vs Volvo S90 - executive car group test

The A6’s cabin has better material substance, but it doesn’t seduce you in the same way, because it’s plainer. The S90’s leathers, plastics, veneers, switches and chrome-effect finishers, meanwhile, are much warmer feeling and more luxurious than the A6’s, although the Volvo’s overall quality levels are less consistently high than the Audi’s. The only cabin that seems in any way dated or unsophisticated is the GS’s, mainly because its fascia, centre console and steering wheel are quite crowded with plasticky buttons that seem a little haphazardly placed.

Then again, a good, up-to-date infotainment system may well inform someone’s decision-making process as much as a premium cabin finish these days. And once more, it’s the E-Class that strikes out into the lead, closely followed by the S90 and A6 – and not so closely by the GS. Our E220d test car had an optional 12.3in instrument screen next to its identically sized Comand Online multimedia screen. Both are backlit to beautiful effect and displayed with apparently limitless graphical processing power and crispness.

In isolation, the S90’s portraitorientated Sensus Connect infotainment system, itself displayed on a piece of 9.0in liquid crystal real estate, seems technologically avantgarde. After the E-Class’s fascia, it’s not quite so striking, but it’s easily second best here. The Volvo system is touchscreen only and incorporates a great many of the controls that might otherwise be cluttering up the dashboard as buttons, so you’ve no choice but to use it.

When it’s clean, the Volvo’s system looks great and becomes easy to use with practice. You swipe up, down, left and right to access different control areas, and expand and minimise other windows as you go. But the display quickly gets smudged and smeared with greasy finger marks, the presence of which lessens the visual allure of the whole fascia. A rotary controller, such as the one in the E-Class or A6, would seem to be worth having, then, if only to save you the job of wiping the screen with your sleeve every couple of hours.

The A6’s infotainment system comfortably pips the GS’s for third, the Audi’s being much more navigable and up to date, despite the superior size of the Lexus’s colour display.

So what about space? All four are broadly roomy. There’s only 30mm between them on maximum driver’s leg room (the E220d having the most) and 40mm on head room (the A6 being the most accommodating of very tall drivers and providing the most telescopic steering adjustment range). The S90 earns a mention here because its sheer size makes for a relatively roomy back row of seats.

I’ve heard that concert roadies always use the same track when setting up the stereo balance of their stadium speaker rigs: Dire Straits’ Money for Nothing. Which, conveniently, isn’t on my iPhone. But I’ve also often heard audio experts using Toy Story by David Guetta to demonstrate the reproductive brilliance of in-car systems – and, as a result, that is on my phone. It’s less of a musical number, more of a collection of random noises arranged into a harmonious sequence at tempo (sorry, Dave), but it certainly gives a car stereo plenty to do.

And in playing it, the E-Class’s  optional 13-speaker Burmester hi-fi fared best, providing a lot more power than anything else as well as excellent range. It was followed by the S90’s 19-speaker Bowers & Wilkins system (excellent at high frequencies and very clear), then the GS’s standard 12-speaker hi-fi (bassy but otherwise ordinary-sounding) and finally the A6’s standard set-up (perfectly adequate but short on oomph). In fairness, Lexus and Audi also offer premium audio systems, but neither car here had one fitted.

Another noise level to report next: how much wind, road, engine and transmission noise fills the cabins on the same motorway surface, in the same weather conditions, at a steady 70mph cruise. You might expect a hybrid Lexus with a quiet petrol engine to rule over its diesel rivals here, but the GS300h’s ride turns out to be conductive and sensitive to an even slightly coarse surface.

As recorded by our decibel meter, the GS300h is actually the noisiest car here, at 66.5dB. It’s beaten by the A6 2.0 TDI (65.5dB), the S90 D5 AWD (65.1dB) and the E220d (64.1dB). The Mercedes’ advantage seems to be mostly accounted for by better wind noise suppression than its opponents. Its engine raises its voice when worked but settles to a remote hum at cruising revs when driven through the tall ninth gear of its automatic gearbox.

And that brings us to some driving impressions. Our four-way test gave us an opportunity to take a snapshot of real-world fuel economy, driving the same route in all four cars at the same time and using trip computers to indicate with a decent degree of accuracy how efficient each is. In our mixed traffic conditions, the hybrid Lexus did reasonably well, returning an indicated and creditable 46.3mpg. Most efficient overall was the A6 Ultra, at 51.8mpg, narrowly beating the 50.4mpg E220d. The wooden spoon went to the S90, which returned only 41.9mpg, a disappointment mitigated a bit by the fact that it’s the most powerful car here, although not by much.

The power outputs of these cars will ultimately mislead you as to their relative performance levels on the road. We’ll keep our impressions pertinent to motorway use, where in-gear acceleration and easy mid-range flexibility are much more important than how fast the cars are from a standing start. And although the S90 backs up its outstanding power and torque outputs with an air of real assertiveness when putting on speed from 50mph, the next fastest option isn’t the next most powerful.

The GS vies with the A6 for the dishonour of being the least potentfeeling car of the group – the Lexus’s hybrid powertrain doing the familiar elastic band impression when you press hard on its accelerator pedal and yet delivering relatively little. The E220d, by stark contrast, puts the gutsy mid-range of its engine and many intermediate ratios of its gearbox to good use and gives the S90 what feels like a fairly close challenge when push comes to shove.

Of this group, the E-Class rides the most comfortably at motorway speeds, allowing supple longwave vertical compliance without permitting much head toss, or any lateral disturbance that might erode high-speed stability. On the 19in alloy wheels of AMG Line trim, that ride isn’t faultless, thumping just a little over sharper intrusions. But the Mercedes’ opponents have more troubling barriers preventing them from handling a typical UK motorway in quite such consummate fashion. For the A6, the problem is a nagging firmness to its primary ride, which often makes the car fidget as the surface under its wheels rises and falls and seldom allows it to settle.

The S90’s ride is the opposite: softer and a bit wallowy, but also quite hollow on the 19in alloy wheels of Inscription trim, allowing those wheels to thump around noisily when they ought to be better checked. The S90’s steering is also mildly unsatisfying. It’s leaden in its control weight, dead around the straightahead and somewhat out of kilter with the rest of the car’s character.

The GS’s main dynamic foible is the peculiar conductivity of its suspension that we mentioned earlier. In other respects, it’s quite a pleasing and particularly calming thing to drive and a fine antidote to the stresses of traffic congestion. Compliant on the motorway and well weighted and paced in its steering, the GS has become a better-sorted dynamic prospect than many might imagine. What it needs is a more rounded powertrain and some better rubber bushings in its chassis to take it from also-ran to real contender. After more than 20 years and four generations of history, the GS may still get there.

And yet it must, for now, come last in our overall ranking. Peerless in heavy traffic and still immutably built in its own way, the Lexus looks and feels antiquated in places, fails to deliver the outstanding cruising refinement you expect of it and hits an unexceptional mark on economy and an even less distinguished one on motorway performance.

The tussle for second is extremely close, and it’s between the S90 and A6. The Volvo’s cabin is more attractive but less spacious up front, and its fascia is less methodically laid out. The S90’s materials are richer and warmer in places but less consistently classy. The S90 is quicker and arguably looks better, but the A6’s ride is quieter, it’ll go much farther on a tank of fuel, and it’s better value. Sensible wins through – and somehow an Audi out-sensibles a Volvo here. The A6 is second.

But our number one motorway car, winning by a remarkable margin, is the E220d. It’s simply untouchable by its rivals in so many ways (on cabin ambience and apparent technological sophistication, rolling comfort and overall refinement) and within touching distance of the cutting edge on cruising economy and outright performance, too. It’s a long-distance machine of genuinely rare abilities. It even has lane-keeping and active cruise control systems that work better than the rest.