PS2, PSP, PS3, X360. Probably in that order. (Don't have a 360 myself, thus the PS3 > 360).
PS2 is one hell of a machine. Lots of great games and currently at almost free prices (over 100 hour games for $5? Count me in!).
PSP is just an excellent machine with great graphics. If Sony hadn't focused so much on the PS3 in the west, the PSP would probably have quite a bit of more content. If nothing else, hit it with CFW and enjoy emulations for quite a few older consoles
PS3 for a fantastic console. Believe it or not, the PS3 has had more playtime from me than the PS2 did in it's time (though it's catching up now that the games are so cheap).
360 for nice exclusives (I've got most multiplats for the PS3, but it's also possible on the 360).
The 3DS isn't that great compared to the DS in regards to game libraries. Just like the PSVita: They're great consoles, but not really at the best they could offer (yet).