The 2005 Hands down. It has traction control, and locking rear differential, and 32" tall tires. The old one only had open diffs, and 31" tall tires.

I've only had nothing but good experiences with the new X. Some of the trails I used to run I no longer bottom on. Also I haven't really found a need for the Locker to climb, I've tired it a couple of times, but I didn't need it.