I would say a fair amount depends on what you want to do with the car. If you just want to enjoy driving and polishnig it, then the newer the better and the Sigma engines are lovely.
If on the other hand you like tinkering and tuning then an early car is better as you can play about with it to your heart's content without having to worry about complex electronics and emissions restrictions.
I bought a CVH engined 4/4 20 years ago and have spent the last 2 decades fiddling with it and tuning it - to the extent of changing the engine to a GM Ecotec unit.. I've had a blast doing it but if I were to buy another it would be a Sigma-engined car without a doubt.
