Well each game is unique. I have played and experienced the highs and lows of each game.
Combat Arms - Good
-Free to play
-Regular Content Updates (however similar to other games they may be)
CoD-Good and bad are exactly what Jabuuty said
- Team game, everyone plays their part
- Big, detailed maps and unique gameplay
- Choice of squad, and ability to spawn near squad members
- Lots of waiting, I suggest that if you are a non-patient person, don't play this game
- Lots of walking/running.