The main reason i got mine is because i liked the games and all my friends have one (besides like 2 that have a ps3 booooo )
I felt the same way for a while. for me mostly, it was because i wanted to play just about any good game. Wii is great and i still play mine, but it just wasn't cutting it. PS3 has a lot of games but its too expensive. with 360, i got pretty much any game that came out plus really really solid and reliable multiplayer. thats why i got one.
What about the Wii? , I don't know, I'm really not a 360 supporter (I own a PS3) but if I had to tell you a reason to get a 360 it would be availibility of games now. Online isn't really comparable at this point, PS3 is getting a revamp, and upgraded servers soon. So if your looking for cheapness in the long run go for the PS3, if your looking for fun now go for the 360.
It depends what kind of gaming expierience you are after, its hard to compare the Wii with the 360, and the ps3 jsut sucks. 360 i reckon is good, cozz it tries to create an entire expierience for the player unlike the Wii which aims at making you have fun. its not to expensive, and its got great potential and a strong line up of games like gears of war, halo 3, cod4 jsut from the top of my head. be prepared for some crpy xbox live service though, its not an unknown fact that servers are down a lot even though you have to pay for the service.
pgr4 - bulldogs game= the best game of hide and seek you'll ever play plus the xbox has got many of the best titles and really good multiplayer
Reasons not to get one: red ring of death blu-ray won the HD war online play costs money no internet browser its really loud