I have to say, stay away from 1000's. Their D-Pad is terrible. Theres a quasifix for that, but its still sub par. And for retro emulation, a responsive Dpad is the most important thing in the world. Also, 1000's have that thing where the square button sits halfway over the screen, which means it only got one stabelizer pin thingy, which in turn makes the square button kinda wobbly compared to all the others.
In addition to that, the screen is the worst when it comes to the ghosting effect - black things, like hair, walls, shadows will always leave a trail when they move on the screen.
I cant judge 2000's and 3000's myself cause I never had one of those, but they both have a better dpad and screen. Though the ghosting is still there on 2000's, its apparently not as bad, while the 3000 traded ghosting for interlacing.
http://www.blogcdn.com/www.joystiq.com/media/2008/10/psp-300-v-200.jpg
the go has the best, though smallest screen, hands down. (its only smaller but it has the same resolution of course). i've not seen any scanlines or ghosting at all. it generally also has the best buttons, they're not the same type you'd find on a ps3 controller with the rubber pad that sink in much. they're like on the first nintendo ds and the gba sp. They're extremely responsive, but give less feedback. They're also smaller which is bad for big hands/thumbs.
Theres no umd drive, but if you play roms on emulators, i'd gather you probably play roms in general, so that doesnt make a world of difference.
The only negative point to the psp go is the L and R triggers. They're hidden out of sight behind the screen and feel weirdly loose, a strong contrast to the face buttons. At least for me, they're really uncomfortable to use. Holding the go so that i can hit both triggers and at the same time hit the dpad and face buttons accurately is almost impossible for me, playing with the analog nub is even worse.
But i might get used to it eventually. Good thing is, even on the snes, few games really require them much.
Start and select are also weirdly positioned and give even less haptic feedback than the face buttons.
Between a 1000 and the go that I own since last week, the go is a huge improvement in every aspect save the L/R triggers and I would say, if you get it cheap, go for that.
Otherwise, aim for a 3000 because interlacing is still better than ghosting.
