Five Cylinders Win the Argument Every Time

The numbers between these two are remarkably close. Both launched at almost identical prices, both sit around 270 bhp per tonne, and both hit 62 mph in under four seconds. If you're shopping purely on spec-sheet terms, the A45 S edges ahead — 421 bhp against 394, marginally better power-to-weight, and £120 per bhp new versus the RS3's £129. On paper, Mercedes offers the slightly sharper pencil. But specs are where the A45 S's case peaks. Drive both cars and the RS3 pulls clear. That five-cylinder engine is genuinely irreplaceable — a warbling, characterful thing that makes every motorway cruise and every B-road blast feel like an occasion. The 8Y generation also fixed the old car's understeer reputation with a properly rear-biased torque-vectoring system that lets you place the car with real precision. The A45 S, for all its ferocious ability, is widely acknowledged to reward admiration more than affection. It's brutal, technical, and occasionally exhausting — a car you respect rather than one you're glad to own on a rainy Tuesday. With depreciation data thin for both, neither has a proven floor, so neither gets a tick in the "safe used buy" column on that basis alone. What tips the verdict firmly is character-per-pound. The RS3 gives you something the A45 S simply cannot manufacture — a soundtrack and a sense of occasion that depreciate even slower than the metal does. Buy the Audi.