I > III > IV > II. If you include the remakes of each generation, I'd have to bump III to the top because it has everything from Gen I, anyway, with FireRed and LeafGreen, which I may like even more than the original, but it's hard to say since I haven't played them in a long time.
Haven't yet played V, but it looks good enough, just wish they'd shake things up or start the series over or something to make me want to get another.

