I'm going to say 360, Wii, PS2, PS3. I do think that the 360, Wii, and PS2 will be very close. All of the guitars out there already will help.

1) PS2
2) 360
3) Wii
4) PS3

PS2 has a massive installed userbase, and a lot of people already own guitars.
360 will have more users than Wii in NA, where GH sells well.
Wii has far more users than the PS3.

yeah, In just bought GH2 for the 360... If the guitar is compatible then I'll buy GH3. If not, then I'll just wait till GH4...

I think there is no doubt on the position of the sony consoles, the PS2 will sell the most and PS3 will sell the least. There is no way this is going to be any other way.

As for the 360 vs. Wii, it will be tough. The 360 has the bigger user base, but the Wii has the casual audience and the price advantage (for those who don't actually have a NG console).

should be an interesting one, but I'm going to give it to the 360.

It all depends on if the current guitars are compatible with GH3.
If they are, then 360 will probably sell more because of the existing guitars...if not, then who knows, I'd vote for Wii.

I'm pretty sure that GH3 will sell the best on the PS2 solely because GH: 80's Edition will only be released on the PS2 (for the time being at least) so a lot of people kept their guitars and wouldn't want to buy one for the other systems.

After that, it's going to be a toss up between the 360 and the Wii. If the new controls on the Wii turn out to be actually good, it will come out on top over the 360, it now, the 360 version will outsell the Wii.

I really don't think the PS3 version will do better than the others because 1) it hasn't been on any other system before and 2) it won't offer new controls to lure people into buying a new guitar.

By the way, do you know that Slash will be in the game ? Last time I said that on GAF no one seemed to be aware of that!

What do you mean by "Slash will be in the game". As a playable character or what?? That would be great in the 80's addition if they had guys like Slash, Van Halen, Petrucci, Yngwie, Satch, Vai and others as playable characters. Totally great.

The Wii guitar looks pretty sweet.

Well, Slash himself said "Actually, I'm in the game, I'm a character in the game..." during an Interview (he was with Matt Sorum). I don't know if he will be a playable character or a Boss (I think yu'll have to beat him to unlock him...). And he was talking about GHIII. He also said the the new single She Builds Quick Machines will be in the game with another tune from the new album Libertad.

You can look on Youtube to find that interview. 

Oh, and from all the Guitarist you mentioned, keep in mind that Slash is the only one to be an official endorser of the Gibson guitars (and of course he's one of the most recognized Gibson users, if not the most recognized one!)... and that he's the perfect Guitar Hero! He's got the attitude

I still remember when the first Guitar Hero was announced along with the Gibson deal that I discussed the possibility of seeing Slash in the game in a French forum! Looks like my dream is finally becoming true!