• Two petrol engines to choose from
• And one fairly frugal diesel motor
• AMG V8 delivers powerful performance

If you’re considering a Mercedes-Benz you’ve essentially got an easy choice. If you want something relatively sensible economy-wise, but still offers a degree of briskness, then the GLS 350 d diesel is the one to have.

However, if you’re in a position where fuel efficiency is of scant consideration then you may be swayed by the ferocity of the Mercedes-AMG GLS 63’s performance.

Mercedes-Benz GLS-Class: Diesel-engined frugality

Okay, it’s not a paragon of low-running costs, but as a seven-seater luxury SUV you would hardly expect the GLS 350 d to prove inexpensive to run.

However, despite being the entry point for the GLS range in the UK, the Mercedes is unlikely to disappoint many buyers thanks to its acceptable blend of performance and economy.

Its 3.0-litre V6 diesel looks a little lost under the GLS’s enormous bonnet, but it’s a suitably butch engine for a relatively heavy car. Packing 258hp and a 620Nm shove of torque between 1,600-2,400rpm, making for effortless overtaking, as well as aiding off-road driving.

Back on asphalt the GLS 350 d has a top speed of 138mph, while the 0-62mph acceleration standard takes 7.8 seconds – ample for most buyers.

Drive is sent to all four wheels via a very smooth nine-speed automatic transmission.

Brutal AMG petrol power

Leaving aside any questions about why you might want such a large SUV to be endowed with such scintillating speed, the fact is the Mercedes-AMG GLS 63 exists. Not only that, its vital statistics take a while for your brain to process. And even when it has crunched the numbers, they still sound extraordinary.

In the engine bay nestles a turbocharged 5.5-litre V8 motor, the source of one of the rudest, rumbliest exhaust notes of any current car. Proper chest-vibrating stuff for those close by.

It cranks out an astonishing 585hp, which together with 760Nm of torque from 1,750-5,250rpm ensures eye-widening performance.

Scorching from a standstill to 62mph in just 4.6 seconds, the GLS 63 powers on to an electronically limited top speed of 155mph.

If that’s not enough – and you’ve the inclination to complete the excellent AMG driving course – this will be unlocked to 168mph.

Again, 4Matic four-wheel drive is standard, but here a seven-speed automatic is the conduit between axles and engine.

• Good roadholding courtesy of air suspension
• Optional Active Curve Control aids nimbleness
• Off-Road Package is effective, but costs extra

You’re never not in any doubt that the Mercedes-Benz GLS is a large, heavy car, so its cornering abilities are rather hampered by the laws of physics.

Despite that, we were pleasantly surprised by both the GLS’s agility and body control exhibited. It feels incredibly solid and assured, offering levels of confidence far beyond the GLS’s common remit of urban school-running.

Sure, you feel a little detached from the driving experience – the focus here is luxurious wafting, not enthusiast-sating handling – but you soon feel confident about its predictability.

We found the steering to be well-weighted and accurate. It won’t please the keenest of drivers with its feedback, but again, this is a seven-seat SUV. The AMG version is be better in this respect.

Every GLS comes with Airmatic air suspension as standard, which allows for Sport and Comfort modes using the Dynamic Select control, and variable ride heights, which means it’s possible to drive through water of a depth of up to 600mm if you’re at the maximum ground-clearance setting of 306mm.

Optional Mercedes-Benz GLS handling packs

Available across the range is the Active Curve System is an active roll-stabilisation package, which keeps the GLS flatter and more composed through faster corners. It does this using some clever adaptable anti-roll bars in a similar way to the S-Class Saloon.

The other optional pack worth mentioning here is the Off Road Package, which nets you a differential lock and low-range gearbox to help tackle rough terrain. There are also three additional ride heights for the suspension along with an Off-road+ mode for the Dynamic Select system.

We tested cars with this package on snow, and found an amazingly capable machine offering almost physics-defying levels of grip and traction control.