Having owned a mk 1 ph 1 and ph 2, mk 2 ph 1 and 2, and driven the mark 3 phase 1, my favourite has to be my current motor, the Mark 2 Phase 2.
Mark 1s were nice looking and riding, but wriggled in faults, the 1.6 petrol engines were rubbish and the gearbox on both of them exploded!
The mark 2 phase 1 was ok, but problems again - the engine went through 2 turbos in 100,000, and was often a case of guess what the electrics would do!
Current car is on 127,000 and still going strong, and is much nicer inside than the phase 1. No faults on it yet except the dodgy CD player.
Have to say I would pick any of them over the other half's Vectra - poor handling, badly built and uncomfortable - even she describes it as a c**p-mobile!
Not sure about the Mk 3, not convinced enough to swap for my Lag (yet