stock for stock, the 24 valve VR6 is the fastest. the 1.8t is cheaper to mod, and has more options. however, if your pockets are deep enough, modding a VR6 (a la FI) will net much more power.
also, you might want to know there are 2 "different" 1.8ts available for the GTI, and 2 truly different VR6's available for the GTI.
Basically, the 00-early 02's had the 150hp 1.8t. they had no exhaust cutout. the 2.5-06 GTi's have the 180hp 1.8t. they upped the power by adding different turbos(the k03sport) different DV and other small changes to the ECU.
Same story with the VR6 motors. Earlier MK4 GTi's had a 12v VR6 that made
(i may be off) 150hp, and around 03 they switched to the 24v VR6 which has 200hp.
many tuners feel the 12v is "stronger" and can handle more tuning than the 24v.
ultimatly its up to you and your pocketbook. having had 3 1.8ts, i can tell you they are great, and very responsive to any tuning.
good luck and keep us posted!
