My take:
Wii: Best for when you people over or parties. Everyone knows about wii sports. But, Mario Kart with 4 people is pretty cool. Also features the nintendo catalog where you can purchase original titles from NES,Snes,n64,Sega,Turbo Graffix16 and Neo Geo. Also compatible with game cube games and controllers.
Cons: HD cables does not make a difference like it does with PS3 and Xbox. Graphics are also a couple steps down. Too many baby games.
PS3: Good for hardcore gamers, if you want a BLU-Ray Player, you might as well kill 2 birds with 1 stone and purchase a ps3. Blu ray hd movie player that also upscales regular dvds movies to HD...It also upscales ps2 games to hd . You can download FREE demos on your ps3. If you own a PSP you can hook up a USB and download PSP demos from your PS3.
This is also the only system of the 3 where you can charge your controllers without purchasing a charge kit. you can buy any external usb harddrive and hook it up loaded with music videos , etc...You can buy any brand 2.5 ata harddrive and upgrade the harddrive size for ps3.
cons: Lower game selection (for now), inferrior to xbox with online game play.
360: Best for the hardcore gamer. Nothing compares to xbox live. More games out at the moment. More downloadable games on Xbox Live. Most shooters are better on the console.
Cons: You have to pay for xbox live. (ps3 and wii are free. ) Does not have an internet Browser.THe elite and 360 requires Microsoft harddrives only- for a 20gig it's $100, for the 120 it's $189. Cant upgrade hard drive beyond 120 GB. Uses outdated DVD format.