Lol this is tough for me...normally I'd be voting for "Z is the best"....chosing between Z's is almost impossible for me >.<
If we're talking real life, I have to go with the original 240, slightly modified (wheels, suspension, slight power bump).
The Z31 is a close 2nd for me. I like the boxiness of it, and ever since seeing what's-his-names 2-tone Z31 in Wangan Midnight, I've had a thing for them
If we're talking about GT6, I have to go with the Z33, followed up by the Z32. Both of these are amongst my favorite drift cars in the game. Both have great power delivery, usable power/torque curves, and with the right suspension setup, handle very nicely. The Z33 can be made to be quite fast as well.
But if I'm honest with myself, the Z34 is by far the best Z in GT6 (IMO, for drifting on CH). With the supercharger, it makes over 550hp and well over 400ft lbs....but it's the curves that really make the Z34 shine. The torque and power come on very early in the rev range, so you have a lot of room to work the throttle, and the deliver stays consistent all the way to redline. The Z34 also has amazing grip in GT6 (compared to the Z33 with its awkward rear spring rates). The chassis makes great use of the power. The Z34 is hands down one of the best drift cars in GT6....it's just my least favourite looking Z