I drove both before I bought my 'beeza' and coming from a 100ps Passat, I knew what to expect with the 1.9 TDi. The 1.8T FR petrol was superb, quick and acceleration was great, the ride was a little harsh compared to the diesel sport, but ultimately I knew that I'd either end up needing tyres every other week or I'd lose my licence in quick time!
Took the diesel in the end and haven't looked back - getting it chipped soon too (up from 100bhp to 150 bhp for £300). Strut brace before that too (cheap at £50).
Prior advice is useful - test drive both and even a 1.4 petrol too (gutless IMO)