I vote 3DS. Wii comes in very close. Then it's PC. After that, PS3, then X360.

PS3 and Xbox 360

3DS

A portable 3D-Gamecube, how can you say no???

There is no such  thing as as a systems that's the "best" for gaming. As long as it has a decent way to control the game (the remotes for "Smart" TVs and the CD-i fail in this regard; plus with the exception of a few games touch only controls only work if you don't need to move the avatar) and there are games for it, the system is "best" for gaming. So all of them. (Except for the CD-i and Smart TVs)

So dedicated game machines(This includes PCs)>machines where gaming is a "feature"

PC -> X360 -> PS3 -> Wii -> Mac -> Handhelds

PC->DS->Consoles (in no particular order) -> PSP -> Mac

Not sure about the 3DS or Vita yet.

Depends on your tastes and what exactly you are looking for. It's a far too open ended question.

PS3 is my main gaming machine though.

The PC, hands down. I think its been like six months or more since I even played any of my consoles.

PS3 is first for me. It's above PC for me because: It's a dedicated system, it's easy to play and use, minimal setup. This applies to games and all other services. No driver updates, no hardware updates, no worrying about whether my system can play a game smoothly, no messing around with settings. Better exclusives.

Don't get me wrong, PC has many advantages over PS3 (and consoles in general) and I know a few of the things I listed as disadvantages may be seen as advantages to others (hardware updates or example). But personally, I'll take the super-easy setup and convenience and exclusives my PS3 gives me over the upgradability, mods and exclusives my PC gives me.

Play both a lot though, infact I'm off to play HL2 now.

Out of all platforms I've played this gen:

PS3>PC>360>Smartphones>DS>Wii

I imagine the VITA will be between phones and 360 once I get it.

DS>PS3>PC>Wii>PSP>3DS>360>Other

3DS is quickly climbing up, but it needs a good year or so before it goes up near the top. (I didn't not combine 3DS ability to play DS, or you would know that would be already on top.)

The reason why PS3 is above PC is that I currently have 9800GT.....that explains itself. 

Given my favorite game that I played this year is Binding of Isaac, which is a PC title.