The answer to this question is not as obvious at it may seem. There are a few things you need to consider before purchasing a game console. Below you will find advice, that will help you choose the best console for your needs.
1. Exclusive games, meaning these games will not appear on any other consoles.
2. Who is it for, yourself, kids or maybe even your parents?
1.) Lets start with the exclusives:
Xbox 360 exclusives:
Halo, Fable, Forza, and Gears of War. Some games have exclusive DLC (downloadable content.)
Playstation 3 exclusives: Uncharted, inFamous, Killzone, LittleBigPlanet, Gran Turismo, Heavy Rain, God of War, Resistance and Metal Gear solid.
Wii exclusives:
Super Mario, Metroid, Donkey Kong and Zelda
The Playstation 3 wins hands down in this category in quality games that you will not get to play anywhere else.
All of the Xbox 360 exclusives will come to the PC, after about six months to a year.
If you are a die-hard fan of the Wii exclusives, then it might be the best choice for you.
So to summarize, best exclusive games:
Playstation 3
2.) The Playstation 3 is good for casual and hardcore gamers. It has the second best online experience of the three consoles. It has motion controller called Move, which is similar to what the Wii offers. It has a built-in Blu-ray player, so you can use it for movies as well.
The Xbox 360 is more for hardcore gamers. Though with Kinect, Microsoft is heavily focusing on the casual market. You have to pay a premium for the online services, but the online offering is the best of the three.
Kinect, hands free motion controlling. This is something that is focused for people who are new to gaming. Kinect games are gesture or voice based and do not require knowledge on how a controller works.
The Wii, pioneer of motion controlling. It is the cheapest of the three. It has poor online features. The exclusives are only worth it if you are a die-hard fan of Nintendo's games. Third party game support is not very good.
With the announcement of the Wii U at E3 2011, i don't think you should even consider buying a Wii at this time, unless you find one very cheap.
And to summarize:
Buy a Playstation 3, If you are a gamer who likes using a traditional controller, you enjoy quality games, free online gaming and you need a Blu-ray player.
Buy a Xbox 360, if you are a hardcore gamer, you don't mind paying for a premium online experience and you don't own a PC that can run the latest games.
Buy a Xbox 360 + Kinect, if you enjoy simple games and not using a controller.
Buy a Wii, if you can find one cheap and you just must have the newest Super Mario, Metroid or Zelda. I would suggest waiting for the new Wii U console coming in 2012.
Now which console to buy according to the audience.
Casual gamers, kids and seniors: Xbox 360 + Kinect
Hardcore gamers: Playstation 3 or Xbox 360, it comes down to the exclusives.