I would suggest you ignore the platform and look at the games which are released for each console. Look for games which match your style of play and find which platform has most of them, and buy that system.
Depending on what types of games you like to play, maybe a console isn't right for you. I have always been disappointed with real time strategy games on consoles. They just don't have the correct interface for it.
The Wii is a very fun system to play with groups and especially kids. The games are easy to pick up and get you really involved in them. It is lots of fun. But if you are looking for real time strategies, or first person shooters its not the best system.
The XBox seems to have the best first person shooters and role-playing type games. There are a few very good studios that write exclusively for the XBox.
I don't know much about the PS3. so I can't compare, but it doesn't look like there are a lot of 'best sellers' that are exclusively on the PS3, at least not that I know of. The PS3 offers other things than a game console though - like a BluRay player so maybe factor that into your purchase decision.
If you come from a PC gaming background, the XBOX would probably have the most games that are similar. As Steve mentioned FPS and RPGs.
The PS3 is actually a great way to get a cheap blueray player. It also, IMO, has the most games -- you should have no problem finding a great game for your favorite genre (as a side note, it really bothers me that the newer PS3 units are no longer compatible with PS2 games, WTF).
As for the Wii, this is a must have if you are a Nintendo fan. For example, you are not going to find a Zelda game anywhere else. This system is must for people who grew up with Nintendo and wants the next iterations of games from Nintendo. It is also a great unit for younger children.
The Wii is a bit of a soft option. I have one, and the graphics are typically lower quality than other consoles. Also, many of the games released are mass produced (due to the low graphics requirements) and some games try to experiment with the use of the controllers, leading to a dubious user experience. That said, the kids like it.
A hard-core gamer friend lives and breathes his XBox, and replaced it despite a 'red ring' ie it died. The graphics are typically pretty good (or great) and the internet play is built-in.
David O'Meara wrote:The Wii is a bit of a soft option.
Absolutely! I vaguely recall reading the Wii was targeted at non-gamers. And it worked. It's the first video game console I've ever owned. And I use it almost exclusively for active games. (Wii Sports, Wii Fit, Wii Resort)
I recently bought a PS3 Slim and so far it has been good. I had considered buying an Xbox, but game forums were still rife with red ring of death problems. Maybe it isn't an issue anymore but I didn't want to take a risk considering that a PS3 Slim comes at $300. But playing FPS games on a PS3 isn't as comfortable as playing them on a PC.
I'm not sure how things are in the Xbox world, but connecting a PS3 Slim to anything other than a TV can be a bit of a pain. It doesn't have a VGA out (I think Xbox does). So to use a computer monitor, the monitor should support DVI-D and you need a HDMI to DVI-D converter. To get 5.1 sound you need a speaker set that takes in S/PDIF optical input. I have two 5.1 speaker sets - one which takes in RCA inputs and the other one takes audio jack inputs. Both are useless with the PS3. Also there are no jacks for headphone/mic.