I know people are going to get angry but, my opinion is as follows.
As far as the Wii goes, it's a solid system, works fine, has few technical issues, and of course has several exclusive games that range from average to excellent. It's capabilities are not quite on par of the other two but it utilizes motion controls that make their games more enjoyable. This is no more evident than the recent Microsoft Kinect and Sony Move.Also its virtual console has many classic games and a couple of good exclusives.
The 360, to me started off as a joke, the sheer amount of technical issues it has is terrible. Not to mention the poor exclusives, not saying there aren't good games on there, but most of them are poorly constructed clones of games already on the 360,PS3, or Wii. There are also others with problems, Tales of Vesperia is a 360 exclusive in America but in Japan it has a PS3 version with more than twice the content. It apparently has excellent downloadable exclusives but I've never seen one, not that they don't exist but I don't know any names in particular.
The PS3 is my system all the way, it had a poor starting, and had been price a little high, but is now crowning itself king, hence the term "Long Live Play". While it has one or two technical issues there are no big ones, it also has the best capabilities. It's exclusives do depend on your preferences but most of them I find to be pretty damn good. It's downloadable games range from terrible to good, but it makes up for that with releasing psx and ps2 games.
The PC is a superior gaming system but it's downside is it's price. Pick your poison.