Difference in PSP Models?

I know more about full consoles, but i really don't have any desire for a lot of Christmas gifts this year, the only thing that really comes to mind is a PSP. I know all about hooking my PS3 up, i was wondering if there was any major difference in the PSPs themselves, the 3000, 2000 whatnot, i would like the god of war pack, but that is a 2000, is there that much difference between the models to even bother with the ratchet and clank 3000? i would like the best model available so i can have it a while and so it wont **** out on me.