Right now I have a Wii as my only next gen system at the moment. I plan on getting the 360 and PS3 as well. At the current moment Wii wise I'm playing Super Paper Mario and Wii Sports. However VC wise I currently have been playing Starfox 64 and The Legend of Zelda: A Link to the Past. When I get the money I'm owned for my grades, I plan on spending most of it on Wii Points cards to get VC games! The only Wii game nearby I want at the moment is Mario Party 8!
However, recently I've noticed that the Wii VC games and retro XBLA games are pretty expensive. Sure all GC games are free to play on the Wii, but if you don't have past Nintendo systems, you're gonna have to pay to play. Also for some games you need the classic controller. Sure you can use a GC controller, but that's gonna cost ya, unless you got it went you got a Gamecube. Some Xbox games are BC on the 360 and can all be used with the 360 controller, but only some are. 100 points on the Wii sets you back a buck, and 100 points on XBLA is $1.25. In some cases the prices for a gen's game are equal. Star Fox 64 is $10, Castlevania: Symphony of the Night is $10. Arcade games are a different story. Though XBLA actually has arcade games, they cost $5, the price for a NES game on the Wii. XBLA has extra features, but in most cases aren't worth the extra money.
So where does the PS3 come in? It can play all PS2 games and all PS1 games, unlike the Wii and 360, of course not all PS1 and PS2 games are exclusive, so that argument is null and void, excluding the exclusives. But how will you be able to play the old games on the PS3? All PS1 and PS2 games can be played on the PS3, and among those are retro game packs. For $20-30 or cheaper, you can get several games that would be more on the VC and XBLA. For example, Mega Man X1-3 would normally set you $24 on the Wii and $30 on the 360. For the same price, you can get that, X4-6, and a Mega Man racing game.
However the thing that pulls the PS3's BC back to the Wii and 360's level is that not all retro game packs are exclusive to the PS2. Some retro game packs can be found on the GC and Xbox, which in turn can be played on the Wii and 360. I don't know if Street Fighter Anniversary Collection is BC on the 360. And with the case of Sonic Gems Collection, some retro game packs aren't even on the PS3. First party Sony games are on the PS3 only, but Nintendo has made far more first party games along with Sega and Hudson Soft, unlike Microsoft. It's just a matter of Nintendo releasing them all. Also while it has more third party exclusives than the Xbox, Sony does not have as many as Nintendo, Hudson, and Sega, which they are releasing. And some games that were exclusive to the PS1, are now on XBLA, such as Castlevania. Retro game packs don't carry all the games that were on past Nintendo, Sega, and Turbographix systems. Finally Nintendo hasn't released games that can be found in retro game packs for the PS2 and 1, unlike MS.
In conclusion, the PS3's BC is better IMO than the 360's. However in the case of the Wii, it comes down to preference of systems, because retro game packs don't cover all the games that Nintendo is capable of putting on the VC.