Well, with your rationale of backwards compatibility, I'd choose:
The Wii - I can play a veritable smorgasbord of classics via the VC, plus all GCN and Wii games.
The DS Lite - stellar library plus all GBA games.
The first gen PS3 - every Playstation game in existence.
The NES - my favorite game system of all time, and I'd have access to those few games not yet on the VC that I love (Bionic Commando, Contra, Rygar, etc). While I also love the SNES, the only game I love that's not available on the VC is Yoshi's Island, and I can play the GBA port on my DS.
Except for a few games here and there on other systems, these four would cover pretty much everything that I really care about.







