Right now as of today Wii is the most fun console because of the motion sensor. But, much of the fun wears off after a couple hours of play. For most people, they will only play games an hour or less after having the console a week or 2. The only game that people play for more than an hour after a week is Zelda. Online play is very weak on wii so far, no games online. News, weather, polls and all that are ok, nothing really great and the browser will cost money soon..... no regular keyboard, headset, etc. will work, they will make people pay for nintendo brand accessories, so it will cost more money in the long run than an Xbox360 or PS3.
Xbox360 as of today is the best online console because xbox live offers more to players. Easier to find friends, easier/more to download from the online service, most games online. The xbox360 probably has the best games so far only because it has been out longest and has so many more to offer. 360 has nice features and power, but also requires you to use many microsoft xbox brand accessories like headsets and hard drives, hd-dvd drive, instead of ones you already have for your PC.
PS3 is last right now because there are not many games out and the online service is not fully functional. IMO PS3 is gonnna make a huge jump to take the #1 spot very soon though. They offer online play for free, Browser is free, the new "Home" which is incredible and the most exciting online experience in console history is gonna be free. The Sony online network will be better than xbox live when it is fully released by the end of the year. You can add PC parts to this machine also, like a 500GB HD later on for homebrew or whatever the future holds for PS3, you can install PC operating systems and just do much, much more with it than any other console. Comes with a blueray movie player, you can use PC hard drives, keyboards, headsets, just about anything, no need to spend more money on stuff that you already have or that you can find cheap at a PC store.