It's a matter of opinion and which "genre" of the game is better.
One opinion:
Modern Warfare 2 if you like the thrill of online gaming.
Gears of War if you like the thrill of playing single player.
All in all Modern Warfare 2 is better
Another opinion:
Modern Warfare 2 is great with online gaming and single player. It is a lot more accurate and "war like"
Gears of War 2 is also fun online and off, as long as you can handle some gore, and monsters.
Call of duty modern warfare 2 is better than socom because with modern warfare 2 you have better weapons and you run faster on the game. I agree it is way better!
Personal opinion. Cod4: Modern Warfare maps are better and the game is more colorful.
Black ops is better
i havent played killzone 3, but i can tell you, cod modern warfare is a great game.
CoD 4 MW
It depends mostly on your taste. If you want more fast-paced action, I suggest CoD, but if you're more into gorey battles and brutal fights, Gears of War is the way to go.
It's all up to your personal preferance but I prefer the modern warfare 2 maps
Yes way better
Call of Duty: Modern Warfare: Reflex
Depends on what type of game you want.
Buy a better game.
Modern Warfare 2 is a better game if you are going to play online.