They could be called the "money makers", because their sales success largely determines the financial well-being of the car firms.
The compacts, or small hatches, are the important models for most car producers - and when it comes time to change, it's an extremely delicately balanced matter.
If a new style of one of these best-sellers is not well received by customers, the losses can run to millions. So the key thrust of design is caution.
This approach can best be seen in the existing Golf models, the lines of which have changed only gradually over the years. The motto of former VW boss Ferdinand Piech had always been: "A Golf must always look like a Golf".
Seen in this light, the now favoured design for the successor to Golf No 4 is almost revolutionary. This new car, the No 5 - to be launched at this year's Frankfurt Motor Show - has a new, elegant and even luxurious form, with trademarket looks taken from VW's flagship Phaeton model. Its influence is set to feature throughout the VW range.
The characteristic features are sweeping curves, plenty of chrome, short body overhangs and indicators integrated in the external mirrors and in the transparent glass headlight units.
Other new features are frame-less door windows and an electric switch replacing the boot handle.
While the overall length of the Golf will not increase by more than 6cm, there will be considerably more space in the interior, particularly in the rear, and a good 30 litres more load space.
VW has also opted for a multi-link suspension, as in the crisp-handling Ford Focus, rather than earlier plans to use a torsion beam axle.
The visual changes will be augmented by a range of powerful engines. The entry level will be a super economy 1.6-litre 115 bhp direct injection petrol engine, which will be introduced this autumn in the Golf IV.
Larger engine options will include a 2-litre direct injection unit developing 140 bhp, a 6-cylinder engine pushing out at least 200 bhp, and even a VR8 is planned. There will also be direct injection diesel engines developing 100, 130 and 150 bhp.
The 200 bhp model will feature in the new GTi when it comes onto the market in 2005, marking the 30th anniversary of the GTi's arrival on the roads of Germany. Initial reports suggest a 0-60mph of 7.5 seconds and a top speed of close to 140mph.
And the cabrio? Nobody really knows if it will be coming at all. It could well be replaced by a canvas-top New Beetle. Or a roadster. Or skipped completely .
In the end, the importance of the Golf was underlined by the announcement that, while the German auto giant expects operating profits to improve significantly in the second half of this year due to higher unit sales, operating profits for the full year will skid lower than last year's.