Here is my view of it.
If your looking for good family games, or party games, or just want to have casual non hard core (most of the time games) and don't want to shell out any money, then get the Wii, although I recommend you have WiFi at your house, or buy the LAN adapter ;P
If you are looking for pretty organized online gaming, willing to spend money to play online each month for one of the greatest communites for the console, go get the Xbox 360, it's totally worth each bang for buck, because their community is great. The only problem is getting used to their console (it's a little confusing at first, but it gets easier as you go along) the GUI or the system it uses is pretty cool too, a plus if you use msn chat/listen to music and play videos.
I don't know much about the PS3, although it is pretty expensive and their isn't really much of an online community... hopefully their will be something coming out soon, but comparing sony to microsoft, they cant pull any big guns out... yet.