We drove the 1.6, 1.5dCi 106 and 1.9 dCi.
Found that I had to work the 1.6 quite hard around town and stir the gearbox too much.
Disregarded the 2.0 on economy grounds, so didn't even drive one.
The 1.5 dCi 106 was amazing for its size. I had this engine in a Megane Sport Tourer and it flew in that car. It coped with the weight of the GS very well I thought, and it's a beautifully sweet unit too. Just felt that when 3+up, it needed a little bit more.
The 1.9 dCi didn't really have much more straightline speed than the 1.5, but where it did score was the way it was delivered. There was a bit more muscle to it, and it felt noticeably more relaxed. If this engine had a pulse rate, it would be about 50 bpm!
The 1.5 dCi we drove also wasn't a great example considering it was up for top money. If it had been a minter, we might have been tempted.