It's hard to place favorites on a system right now, because I'm a complete RPG Gamer. This new main system generation is strangely devoid in RPG's, unlike the last gen.
The Wii is a fun system, and it has it's games I love: Okami, Tales of Symphonia: Dawn of the New World, Brawl... However, 'sides these it really lacks in much else. There are just no games out for it that I'd buy besides the ones I listed, and I have those.
The PS3 is, again, very lacking in good games I'd play. In fact, this one is even more lacking in the RPG and Adventure department then the Wii is. I pray to good Final Fantasy will update soon. I can't live off of Eternal Sonata forever. -.-;;
The 360. Now, I'm no Xbox fan whatsoever, but I have to say, they've had some wicked good games so far! Tales of Vesperia was epic, Eternal Sonata was great before the remake came out, Infinite Undiscovery looks very fun, and then there is the new Star Ocean. There's way more then I listed, but I'm really impressed with the games this system is getting.
I own both the Wii and the PS3, and I can't pick between them, but the 360 seems to outclass those so far. I can only hope the other two systems can start living up to their brand. I need more good games like Tales of Symphonia, for the Gamecube, to be released. ^_^