I stopped playing Pokemon after Ruby and Sapphire (it took a while, I wanted Leaf Green and Fire Red but couldn't afford them, even though since I'm 18 now then when they were out I'd have been about 15/16, so I should have been out of it by then anyway, but I soon gave up on Pokemon after that). However, to be honest I wouldn't mind downloading some of the later ones for a GBA/DS emulator, so I can see if they are actually any good. I wouldn't spend money on them though, but I suppose for casual gameplay it'd be fine. Anyway, since I like to be an all rounder then my party would probably be from the earlier games (pre-Fire Red/Leaf Green only):
1. Pikachu (of course, although Raichu would be acceptable too)
2. Pidgeot
3. Flareon
4. Blastoise
5. Espeon
6. Umbreon
(Yeah, I was a bit of an Eevee fan, but I wouldn't choose an all Eevelution squad, I think that variety is best and allows for more adaptation, in a way...)