The lights are on
Really, cut the Wii right out of the picture. Yes it does have more family oriented games, like New Super Mario Bros. Wii, but that is mostly it. MADWORLD and No More Heroes is basically the only "hardcore" or Mature games out for it. And the Wii just doesn't have any good online. Nobody bought Wii Speak, you have to know the person you're playing with in real life to play with them. The only real plus is the motion controls which have now gotten even better with MotionPlus!
Next you have the PS3. It has so many features. It is cheaper in the long run than the Xbox 360. With Blu-ray capabilities, it can do more than play beautiful movies, but also have an advantage on graphics when playing games. Because of this, the PS3 gets more exclusives because developers want to make their games look the best they can. The place were the PS3 falls is the online. With the free online, it does get many inhabitants, but the 360 has the advantage here. But it does have a big advantage over the 360 and it is making people switch over. What is it you ask, it is durability. The 360 has the RROD and it kills off so many 360s. Even when your system dies, they have acceptable customer support.
Finally the 360 is the final one I will talk about. The only thing it has over the other consoles is online play and its social capabilities. So many people got the 360 when it originally came out, so their friends would want to be able to play with them when they have the chance. This causes a chain reaction because people know that the online doesn't fall. There is still the thing about paying for online gaming though. Otherwise, the 360 would be a loser. It doesn't get many exclusives. It gets Halo and Left 4 Dead, but that is about it. It doesn't have an graphical advantage over the PS3 in anyway, shape, or form. Most 360s last 6 months to 1 year before they get the RROD and then they're toast. With horrible customer support, most people switch after their second or third 360. Then all the accessories cost way too much money. It still costs $80 to get a Wireless Adapter, even with the recent price drop.
Overall, it is your decision. I think that PS3 is going to become the leader within the next couple of years.