i have both (as im sure alot of others here on the forum do aswell)
i have barely touched my wii (giggle) in a while, they havent released enough good games (or at least games that make me wanna rush out and buy them)
there are good games in the pipeline, but for them you need patience waiting for their releases....360 has a load of excellent games out already, plus you can play your xbox games on it (or buy some old ones if you dont own an xbox). basically the 360 has a massive selection of games to choose from, the wii doesnt.
both are good systems, but i think overall the 360 will keep you entertained for longer. with the wii you may get bored of it until the big titles start coming out