If you have a 360, then for god's sake get a Wii because the PS3 had the same games. If you don't then you'll just have to listen to everybody's opinions. Owning both systems, I can safely say the Wii is much better than the PS3. The Wii had more good exclusive games, and they both tie in good games if you count multiplatform games like GTA4. The PS3 had better online with most games, but to my knowledge the Wii has more cool stuff to do when you get online. With the Wii Shop Channel letting you get old Nintendo games from the Nintendo 64 era and before then.
Great games for PS3 that I played:
Ratchet Future: Tools of destruction
GTA4
Great games for Wii that I've played
Super Smash Bros. Brawl
Super Mario Galaxy
LOZ Twilight Princess (rented the Wii version and liked it, but own the Gamecube version)
Metroid Prime 3: Corruption
Bully Scholarship Edition
Resident Evil 4: wii Edition
Resident Evil: Umbrella Chronicles
Decent games for PS3 that I've played
Army of Two
yeah, that's it.
Decent games for the Wii that I've played
No More Heroes
Mario and Sonic at the Olympic games
Super Paper Mario
Mario Kart Wii
House of the Dead 2&3
Keep in mind that my definition of "decent" means definitely worth playing. Just not an excellent game. I was about to give a list of the console's games to come, but I've yet to see Sony's E3 presentation of games to come. So we'll put that aside.