Eternal Sonata and Bioshock (both 360) because they were exclusives, at the time.

Okami on PS2 because I wanted to play it in its "original" form, and I prefer the PS2 controller.

Ocarina of Time on N64 because I wanted the whole original experience, I didn't want to play it on a disc with a different controller. I wanted to play it as it was intended to be played!

hell yeah.

- PC for multiplat cause it's cheaper on Steam, and I can fully customize interface and so on for a better gameplay/visuals experience (except Oblivion that crashes for no reason at all. Couldn't play more than 2 mn ^^)

- Wii for the Wiixclusives and VC/WW titles

- I intend to buy a PS3 soon, mostly for its JRPG exclusives

All my Ps3 games on the Ps3 because its the only system i have. 

I keep a franchise to the same console brand. So Assassin's Creed/Bioshock goes to Xbox, Resident Evil/Final Fantasy goes to PlayStation 3 and so on. Anything "new" like Dead Space, Batman, Dragon Age goes to PS3 more often than not unless it's a shitty port. I find DualShock better for most genres, this being more important than a couple less frames per second or missing pixels.

COD 4 modern warfare - i prefer shooter on ps3, 360 controller is too big for my hands, online free       

COD modern warfare 2  - the same as COD 4

PS3 for the exclusives and trophies and the majority of my friends owns a ps3

360 games

Gears of war 1, 2 and 3 - for the single player, (i refuse to pay online)

Dead rising -     for the single player, fan of zombie games.

Bah, it ate my long ass post. Im not retyping.

1. Mass Effect (360)- It came out on the 360 months before there was a pc version and I prefer consoles to the pc

2.  Mass Effect 2 (360)-  I had already completed the 360 version of ME 1 so I could transfer my data into ME 2 on the 360

3.  Final Fantasy 13 (PS3)- It was the best version and it's as simple as that 720p with 1080p video vs 576p with 720p video

4.  Eternal Sonata (360)- It was on the 360 first and I don't sit and wait to see if a game I want is going to land on a preferred system like many people seem to do.

5.  Tales of Vesperia (360)- It was on the 360 first and apparently it's the technically better version since it runs in 720p while the PS3 version is 640p

6.  Street Fighter 4 (PS3)- Technically the 360 version is better since it's a higher resolution but the dpad on the PS3 is so much better for fighters

7. Resident Evil 5 (360)- The 360 version had better anti aliasing over the PS3 version but the deal breaker is when the demo was released on xbl before psn so I had got use to controlling the game with a 360 controller

8.  Dragon Age Origins (PC)-  As I said before I am primarily a console gamer but reviewers and anyone who had seen and played both versons recommended the pc version highly over the console versions.  There is a fine line between preferring something and being loyal to the point of bordering on stupid. 

My room mate recently got the PS3 version of the game since he doesn't have a pc that can run the game and the gameplay and graphics does seem to be miles ahead on the pc version.

9.  Ninja Gaiden 2 (360)- see number 4 for explanation.  Also NG2 on the 360 has more gore and is more challenging than the PS3 version.

10.  The Last Remnant (360)- I did not have a pc that could run the game fluently at the time but apparently my 360 can't run the game fluently either.

Edit I forgot some)

11. Borderlands (PC)- It was very cheap on steam during the summer sale

12.  Need for Speed Undercover (PC)- It was very cheap

13.  Prince of Persia (PC)- cheap

• Dragon Age: Origins (PC) - Vastly superior version
• Left 4 Dead (PC) - Best version, vastly superior multiplayer community
• The Orange Box (PC) - best version, vastly superior multiplayer community
• The Elder Scrolls IV: Oblivion (PC) - mods
• Unreal Tournament III (PC) - $10 Steam sale
• Red Dead Redemption (PS3) - free DLC
• Bayonetta (360) - best version
• Borderlands (PC) - best version
• Call of Duty: Modern Warefare 1 (PC) -Best version
• Call of Duty: Modern Warfare 2 (PS3) wanted a local MP shooter, no dedicated servers on PC
  
• Bioshock (PC) -$10 Steam sale
• Mass Effect 1 (PC) - 360 version is mediocre
• Mass Effect 2 (PC) - Wanted to transfer ME save file
• The Force Unleashed (360) - $8 at a local used games shop
• Fallout 3 (PC) - Mods
• Final Fantasy XIII (PS3) - best version
• Batman: Arkham Asylum (PS3) - free DLC
• BlazBlue: Calamity Trigger (PS3) - 360 controller sucks for fighters

I don't really own very many multiplats. They tend to interest me less than exclusives.

ME 1/2, Elder Scrolls: Oblivion, Borderlands, Fallout 3: (PC)   Games of this nature just do not feel right to me on a console.  I started as a PC gamer, and I have always internally called "Western" RPGs, Computer RPGs.  They just feel right here and have never really felt right on a console.

All FPS games: (PC)  I hate playing shooters with a controller (oin both the 360 and the PS3) so I do not buy any of them.  Move might change this, but I doubt it.  I am a keyboard and mouse kind of guy all the way.

DragonAge Origins: (PC/PS3):  Yes, I ended up with both (one was a gift) and ended up beating both of them .  In the end, the PC version was far superior, tho I cannot say that I didnt enjoy playing DAO with a controller (which really suprised me)

Eternal Sonata: (PS3) It is more colorful, has added content/characters and well I just prefer JRPGs on my PS3. 

All Fighters (PS3): They just play better with the PS3 controller than the 360 controller.

Sports Games: (PS3) Same as above.  Never enjoyed playing these with a keyboard/mouse.

My usual rule of thumb: PC first and formost, PS3 and Xbox for exclusives.  If it is on both consoles, I usually go with the PS3 version unless (like Bayonetta) there is a gifuckingnormous difference.  The PS3 controller just fits better in MY HANDS than the 360.   This by no means, means that I think it is better, It just feels more confortable to me.

This gen I have a Wii, PS3 and a DS, because they rarely share games I don't get a choice really.

Last gen I had both a GC and a PS2, as I far prefered the GC controller so I would have bought multiplats on the GC.  However the only multiplat I bought last gen was Tales of Symphonia and the PS2 version was never released in Europe