First of all lemme state that there is no hard or fast rule on what is better or not. At the end of the day it all depends on the player's individual ears.
The diff between the new and old version of the GT-2 is that the older GT-2 California mode is based on the Mesa's Mark series amp whereas the new model is based on the Dual Rectifier.
IMO the older model sounds much "sweeter" and less grainy which I prefer. There's also more "warmth" to it and when coupled it with an EQ pedal during solo pieces, its the lead tone that I seek in a pedal.
Kinda sad when I had to let the pedal go though...
