my psp 1001 died, cracked screen; R.I.P. 12/31/05 - 11/06/08. jus got a 3000 w/ warranty !
Okay, my breakdown is something like this...
Jak 3 is probably more fun, has some fun weapons, and the new city is much cooler IMO.
Jak 2 is much harder, but opened for Jak 3. Haven city is much bigger than in Jak 3, but if you hit a guard with a car or anything (the roads are busy. If you go high, you'll probably bump into other zoomers, and if you're low you'll probably hit guards if you're not careful) or hit a civilian within a guard's close sight, guards will begin to pursue you. Just keep driving and they'll stop.
I would buy Jak 2. It's an excellent game. I like Jak 3 more because of the weapon upgrades and it's a little easier, but other than that, Jak 2 is better.