What do you mean with good competition?
Playing against someone, have a great match and saying "gg" at the end? Well, that must be totally the same.
If you mean the most "pro gamers" - without a doubt on 360.
Look at the teamladder on gamebattles.com (I know, some of you probably don't like it, still the biggest league!)
Xbox 360 CoD MW3 Team ladder: Total Teams: 33,910
PS3 CoD MW3 Team ladder: Total Teams: 8,925
Team ladder EU:
360 Total Teams: 7,700
PS3 Total Teams: 3,570
Imagine not having GamePass on your console...