Worst
Has to be my grandfathers escort van - non turbo-diesel. Felt like it was powered by elastic bands and the brakes did f-all.
My old man had a Volvo 340 for a while. Cripplingly uncomfortable seats, wider wheels and no power steering. Took 2 of us to turn the wheel at parking speeds.
2005 Audi A4 2.0TDi auto. Did everything almost too well and so ended up completely characterless and dull as fck. 80mph felt like being sat in front of the TV with the sound off.
Best
Technically it should be the Audi RS4 Avant I had to deliver across London, but I walked away feeling disappointed. I suspect it would be great on a mountain pass in the Alps, but at sub 30mph in London, it was just pointless.
Fiat Cinquecento Sporting. All the build quality of a wet paper bag, but it handled really well and you could thrash the knackers off it in everyday driving.
My VW Passat estate. I've done almost 100k in it (total 180k) and it's been solid, reliable and efficent. Comfortable motorway cruiser, but it's also been ragged over a few mountains when fully loaded and has risen to the challenge. I would like something that has a bit more life to it though...