Battlefield 3

Battlefield 3 is better than every casuals' dream Modern Warfare 3. This is a fact and therefore cannot be countered in any way.

Dem graphics
The graphics are really good on the PC version, and because everyone cares so much about PC, that means that they must be better on every other version, right? Right. Graphics are a really important part of the game, because if there are better graphics then you can see the enemies better and it means that the game is better. It's simply irrefutable logic that only a Modern Warfag would attempt to rebut.

It was made for PC
PC Master Race got a FPS tailor made for them. They get to use Origin, which is a really cool spyware-free online play framework which is totally bug-free and user-friendly.

Because it was made for PC, it's obviously better than Modern Warfare 2 3.

It's not a copy paste
If you bring in some features from a previous game in the series, then the whole game automatically becomes shit. Again, irrefutable logic only a Modern Warkid would try to go against.

Hence Battlefield 3 is so good. Stuff like the minimal building destruction and drivable vehicles is really new and innovative, as well as the Frostbite 2 engine which is totally new and absolutely different to the Frostbite 1.5 engine in Bad Company 2.

The fanbase is really mature
The Battlefield 3 fanbase is one of the most mature fanbases in the world. They don't seem afraid of any other games that may threaten BF3's sales figures at all, and never complain about any rival games. They're really nice people and make the game so much more fun to play.

As opposed to the CoD kid fanbase, all of whom are prepubescent knobends who sing down their mics on their Xbox 360s.

Conclusion
So as you can see, Battlefield 3 is the better game. Anyone who goes against this is probably paid by Activision to do so, or is a 12 year old child.