Gaming Heaven...

[Skyblade]

Well, that makes this easy.

GameBoy
SEGA Nomad (beating out the GameBoy Color, despite the battery troubles)
GameBoy Advance
Nintendo DS (the PSP is great, but most of its good titles are ported Playstation games)
Nintendo 3DS (poor Vita not getting enough games, it needs more than five good titles, especially when two of them are ports)

I'll do full consoles later.

Edit: Bolivar's handheld list is obviously trolling, there's no way anyone can take the PSP and Vita seriously over the DS and 3DS. Heck, the 3DS got more top quality games last year alone than both others have had combined during their whole lifespan. I like the systems, but they don't have the games.