If it's not on the Wii then it's not a classic.

http://marketplace.xbox.com/en-US/games/catalog.aspx?d=6&r=-1&g=3019&mt=16&ot=0&sb=0&rl=1&p=1

Here you can see a list of Classic games available on Xbox360 marketplace. There are 60 games listed. Here are some highlights:

• Sonic 1 / 2 / 3
• Golden Axe
• Banjo Kazooie / Banjo Tooie (I know after 16bit, but hey... BANJO!)
• Castlevania
• Fatal Fury
• Metal Slug
• Phantasy Star II
• Pac Man
• R*Type
• Streets of Rage
• Street Fighter II HD
• TMNT
• etc

If you want to stay legal AND play online AND have the best classics, all you have to do is download the classic games on the Wii's Virtual then download the ROM on your PC and use an emulator for online play.

If you don't care about being legal, just do the later part.

Wii. 'Nuff said.

You'll need both MAME and a frontend for it, yes. The main MAME program is open source and free to download. There are many frontends, with different interfaces and abilities to organize your collection of games.

Google can help you more than us, though, because even if most of the old arcade games are abandonware for all purposes, the legal state of their utilization is sort of a grey area.

Easily the Wii. Its the only reason I have considered buying one because of just how awesome that feature is.

Wii, by a large margin. But no online play on the classics.

If you want classics with online play you'll need an X360, but you can count all those XBL classics with online by your fingers. The rest are new games or remakes. Not the classic untouched games.

So 3rd party online classics go to the Xbox360.