Alfa's Mito is also a relatively conventional hot hatch, and has the innovative Multiair engine. Just 1368cc, it produces 133bhp and emits 129g/km of Co2.
In the cars
You sit low in the Honda, and it's spacious up front. But there are restricted views over the shoulder and behind, and the rear seats are useful for luggage only in reality.
The engine's eagerness, the short-throw shift, the sporty driving position and a firm ride all encourage spirited driving, as does the limited roll, plentiful grip and steering that's quicker than the Insight's. The chassis, though, is still disappointingly inert.
On a B-road it is mildly entertaining, even if its performance rarely rises above brisk. The real fun is to be had from its instrumentation, and the miserly games they allow.
The BMW also allows numbers games - albeit via an old-school, needle-swinging econometer. But the real fun comes from the surprisingly strong performance - determined acceleration comes from 280lb ft of torque that overcomes the tall gearing.
The BMW needs pushing hard to bring it alive, but it achieves its pace with civility, the well insulated cabin giving a premium aura that neither the Mito or Honda achieve.
The Golf GTD is also civilised, and fun. Press the Sport button and it's quick (0-62mph in 81.sec) and handles B-roads with aplomb.
The Alfa is the cheapest car here, and it's better for having the Multiair engine, which is refined and fun. But that sophistication is undermined by a crashingly turbulent ride, somewhat crude handling and weirdly springy, if quick, steering.
Throw in a mushy gearchange, a not-really-premium dash and hard-to-read instruments and you have the least polished vehicle here, by some margin. The Cloverleaf remains the Mito to have.
The Mercedes is as surprising as the name is long. The powertrain delivers the kind of zest you'd expect from an engine 800cc larger. True, its 0-62mph time is the longest here, but on the road its low-revving, steam-train torque and smooth delivery are beguiling.
This dynamism blends with the usual subtle Benz attributes of no-nonsense comfort, space, practicality and aura of robustness.
Real world figures
Only one car failed to break 40mpg - and the Alfa's 38.7mpg is still pretty good considering.
Next came the Honda, at 43.1mpg, the Golf at 43.3mpg, the Merc at 46.7mpg and then the BMW, which topped 50mpg.
The 320d is the most rounded car here - but not the most entertaining.
That prize goes to the Merc, for its unlikely mix of economy, performance and deft handling, all in a big car. It appeals as much for the unlikliness of its performance as its competence.
It's closely followed by the Honda which, despite its flaws, remains a deeply appealing package for its style and verve.
The Golf is more of an all-rounder, but its appeal and practicality could be enhanced with efficiency measures like stop-start and driver aids.
That leaves the Alfa, which is strong for visual and emotional appeal, and for its innovative engine.
The full story is available in Autocar magazine, on sale now.
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