When we reported on Audi's magnificent A8 4.2 V8 FSI last week, we couldn't escape the fact that BMW's 7 Series and Mercedes-Benz's S Class were its main rivals and that Audi, for a while, had no diesel derivatives compared to BMW's 730d and Mercedes-Benz's S350 CDI offerings at the lower end of the price band

, a fact that in our minds limited the A8's sales volumes quite a bit. Audi resolved the matter a few months ago by not only introducing a range-topping 4.2 V8 TDI model to the A8 range, but also a 3.0 TDI derivative that will surely help to increase A8 sales in the long run.

However, regardless of how highly we rate the A8 as a range, it's the Mercedes-Benz S Class that remains the undisputed ruler in terms of sales volumes and, unlike the Toyota Corolla, it's not because people have no taste and are blindly buying something they perceive to be a quality purchase. No, at this price point, quality is a given, which means I can only speculate about why the S Class is consistently more popular than its competitors, who offer similar levels of quality, luxury and specification. The only reason I can imagine the S Class to be so popular is because of its reputation, something that was established long before the 7 Series or the A8, as they're known today, was even conceived. The S Class has for decades been the epitome of "having arrived", offering a tangibly stylish and stately means of transportation for the crème de la crème of the world.

In the local context, you will undoubtedly see more S500 and S350 models on our roads, a large portion of them thanks to our government's persistence on buying new ones every few years and their uninformed preference for petrol-powered models. While these cars are great, it's not my favourite S Class and, in my opinion, also not the one that should be on top of your list. No, the best S Class you can possibly buy in the astounding S350 BlueTEC. Yes, it employs several of the now-familiar BlueEFFICIENCY measures as well, but this one – the BlueTEC – is extra special.

Before you get completely confused, let me explain the simple difference between BlueTEC and BlueEFFICIENCY. BlueEFFICIENCY is a culmination of efficiency tweaks and technologies widely used by manufacturers aiming to reduce emissions while improving economy through various measures such as lighter, more efficient and less power-hungry components, along with supporting design cues and fuel management wizardry. Think of it as Mercedes-Benz's answer to BMW's EfficientDynamics.

BlueTEC, in turn, refers to unique innovations developed by Mercedes-Benz, such as "simulation technology", which goes further in reducing harmful gas emissions by performing far more intense analysis of the engine's operating parameters and applying adjustments thereto, while also making use of new componentry such as a three-way catalytic converter, SCR (Selective Catalytic Reduction) and NOx storage catalytic converters and particulate filters. Read more about the technology here.

As such, the S350 BlueTEC is what many people would call super-efficient. Our sparkling white test model was fitted with an AMG sports package, making it look like an AMG model, but whether it's in standard form or fitted with such a package, the S350 BlueTEC looks just like any other S Class: no strangely-designed alloy wheels or anything to set it apart as an efficiency model, just a "BLUETEC" badge on the bootlid and a small BlueEFFICIENCY badge on its flanks. There's value in having it look the same as any other model in my opinion as I've always believed that so-called efficiency models need not look like something from outer space.

I won't elaborate too much on the car's styling in general as styling is a highly subjective matter, but suffice to say that the S Class is very good looking. What is slightly off-putting is Mercedes-Benz's grotesque adoption of LED lighting technology on the S Class. Audi obviously made it popular, but on the S Class, it's too much (52 LED lights in each taillamp, for example) – a small, tasteful strip down low on the bumper (think E Class) would've worked much better.

As mentioned, luxury and high specification levels are a given in a car of this stature and the S350 BlueTEC is no exception. Safety features have been enhanced with new features such as Active Blind Spot Assist (actively signals and controls vehicle in circumstances where a vehicle is in a driver's blind spot) and Active Lane Keeping Assist (applies braking to guide vehicle between lane markings). Unfortunately, many of the things I'd really like in my car is only available as an option, such as the high-spec Bang & Olufsen BeoSound AMG system with its impressive 1200 watt, 15-speaker arrangement that offers a concert-quality auditory experience.

Mercedes-Benz is of course a master of V6 diesel engines, which means that the 3.0-litre V6 turbodiesel engine doing duty in the S350 BlueTEC is a gem. It develops 190kW of power and 620Nm of torque, mated to a seven-speed automatic transmission. While acceleration to 100km/h takes 7.1 seconds, there's no overtly noticeable compromise between power delivery and efficiency – in fact, this engine is 35% more powerful than the one it replaces. Top speed is an electronically limited 250km/h.

Mercedes-Benz claims 6.8-litres/100km in the combined cycle and carbon emissions of just 177g/km, making it 0.8-litres/100km and 22g/km more efficient than its predecessor. I could not get anywhere near Merc's fuel consumption claim (interestingly, it's identical to BMW's claimed consumption for the 320d EfficientDynamics) but was still thoroughly impressed with the 7.6-litres/100km I managed on the open road (it went up to an average of 8.2-litres/100km in urban traffic). It's a consummate cruiser and superbly comfortable, but in my mind doesn't feel as dynamic as either the BMW or the Audi – in fact, as will all my Mercedes-Benz experiences bar the SLS AMG, the car forces you to drive in a manner that complements its feeling of wafting along.

The S350 BlueTEC retails for R1 034 880, which includes a 6-year/120 000km MobiloDrive maintenance contract and a 2-year/unlimited-kilometre warranty. The BMW 730d, with 180kW, 540Nm and fuel consumption of 8.6-litres/100km, retails for R970 959, while the Audi A8 3.0 TDI Quattro Tiptronic, with 184 kW, 550 Nm and fuel consumption of 7.92-litres/100km, retails for R924 500. Lexus offers no diesel models and Porsche should consider introducing a diesel-powered Panamera, considering how the Cayenne diesel is the best seller.

The Mercedes-Benz S350 BlueTEC is undoubtedly a superb car with good performance and exceptional efficiency. The BMW appeals to a more specific type of driver without offering anything more than the Mercedes-Benz despite a better price tag, while the A8 3.0 TDI, as with the 4.2 V8 FSI, offers a superb balance between the two (not to mention the best price tag and fuel consumption), making it my choice of the trio. However, if it had to be an S Class, I'd take the S350 BlueTEC without thinking about it twice.

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