The Wii wins out here for me.
In terms of exclusives, the Wii is the best without a doubt. Donkey Kong Country Returns, Metroid Prime 3, Super Mario Galaxy 1/2, Sonic Colors, Xenoblade, Monster Hunter Tri, Smash Bros. Brawl, Rhythm Heaven are all amazing games. Those games collectively kick Uncharted and Halo to the curb. And that's only a couple of the games available. WiiWare was pretty great too with the Bit.Trip games and others.
Motion-controls also brought in a big wow-factor of mine when I first bought the console. The fact that I could make a swinging motion and have that mapped in a tennis game was unheard of before. Even apart from the wow-factor, it did help with certain games. Pointer controls are superior to the analog stick in practically every way. Golf games suddenly became fun with motion. Games that use swords such as Red Steel 2 and Skyward Sword simply wouldn't be possible or work as well with a regular controller.
The PS3/360 generally offered the same games. Once I got a decent PC, I didn't see any need for them. After all, all of the games worth owning one for (Deus Ex: HR, Arkham Asylum, Portal 2, etc.) were available in their superior version on the PC. The Wii was unique in that it offered games that couldn't be found elsewhere and were unique to the system. The fact that it was underpowered may have also been a blessing instead of solely a liability in that it forced developers to create unique games for the system.