Well, the Wii should be in a different category from the PS3 and the 360. The types of games they offer are usually Wii exclusives. You're not going to see Halo or COD or MOH on the Wii, but you'll see plenty of fun, intuitive games that none of your friends are playing. As such, its been tagged with a "kiddy" label by the more "hardcore" gamers out there.
Really, it comes down the the 360 and the PS3 as most of the new big games are geared towards these two consoles only. Graphics wise- eh, I think they're pretty much interchangible. Though the PS3 seems to offer a bigger color scheme, the 360 seems to have more clarity and detail. Sound is a non-issue, they both sound great.
PS3's Blueray vs. 360's HDDVD? Well, we know who won that war but also look at the fact that right now you can buy HD DVD's for a fraction of their original cost. They look and sound the same as the Bluray versions, but you can buy almost brand new titles for around 2 or 3 bucks. Three years from now your Bluray player on the PS3 will be negligible once you can buy them from Wal-Mart for twenty bucks like you can a DVD player.
Exclusive titles? 360's got Halo, PS3 has Final Fantasy. Take your pick, even though both franchises are playing coy about overlapping onto the other consoles. Right now, it's a safe bet that you'll only see Halo on the 360.
Online play? No question, the 360 is the only console right now that offers anything resembling decent online play. The PS3's trying, very hard, to get its foot in that door but only time will tell.
Downloadable content? DC on the PS3 is few and far between. I actually believe the Wii to be the superior choice of the Big 3 right now, with classic downloadable games going for pennies on the dollar. ps3 and 360 could learn a lesson here from their little brother.
Accessories/periphrials? the 360 has them, good luck getting them to work. Ps3 currently out to lunch. Wii? More unnecessary add-ons than you could shake a stick at!
Reliability: to me this is an overlooked area of system performance. I want a solid console that's going to outlast me. The 360 is an epic failure in this regard, their heat shield problems make them the GM Intake Gasket fiasco of the Next-Gen consoles. Wii's aren't recommended for households that smoke indoors. The PS3 wins this one, hands down.
Future backwards compatibility:
This is what I have to offer on BC. The PS2 games on the PS3 look horrible. DO NOT throw or give away your PS2! Save it, as you'll figure out soon enough that playing an old favorite looks like it was taped off of Broadcast TV in 1983 with a Betamax. The PS3 has an entirely different processor built in just to play PS2 games, though it was added as more of an afterthought and handles the resolution at half the rate at as a regular PS2. It's convenient, and its a selling point, but it's not quality.
Historically, Sony has kept the just replaced console still full of new games long into the new consoles life. You could still buy new PS1 games for a year or two after the PS2's introduction, likewise I just bought Quantum of Solace last week for the PS2, with more games set to come out well into next year. That's what, three years of the pS3 being around and we're still getting new games for our old consoles? That's pretty sweet, in my book, for the folks not ready to jump on the new bandwagon as soon as it comes out.
Microsoft fails in this regard. As SOON as they announced the 360 regular X-Box users all heard the funeral hymn. It was literally "upgrade or die". Not very consumer friendly.
Longevity: The PS3 has an estimated lifespan (by Sony) of no less than eight years. (The PS2 will have been the longest lived of the consoles, clocking in a full 11 years of active development by the time Sony pulls the plug. Compare to the four year life span of the XBox.) Microsoft has announced a tentative five year development of the 360, so prepare to squander your earnings in another three or four years if you settle on the 360.
Price? Well, if you can find a Wii, 250 Bucks. A 360 with a 20 gig HD (stay away from the "Arcade Edition" for 250.00) will run you about three hundred. A PS3 goes for 399.00- so take your pick. IMHO the PS3 will have to come down to stay competitive. The 600.00 price tag when new greatly hurt its initial sales, and as such the price dropped two hundred bucks. So we'll see.
Image/Popularity? Everyone I know owns a Wii or a 360, or both. PS3 has the "tired old man" rep right now being that their best sellers are WWII FPS and Metal Gear with 20 minute cut scenes. People want to shake and shoot, so if you want to be able to play what your friends are playing, grab a Wii-mote and a 360 headset.
So overall? I'd say the Wii is a sure bet, a given. Between the 360 or the PS3? I would say the PS3 offers the best long term option, but the 360 offers more right now than the PS3 does. So take your pick.
Or, like my buddy says, "It's a question of whether or not you want to play Halo."