BO2 was the best.
The map design
Pick 10 system was GOAT
Score instead of Killstreaks to reward objective play
VSAT - Dogs - Swarm at the same damn time
BO2 had so many great additions and innovations. You want 6 perks go ahead. You want 1 perk and 4 weapon attachments go ahead. You can do whatever you needed for your play style.
Weapons were well balanced.
The game easily had the least amount of camping. You didn't play the objective you weren't getting streaks and definitely wouldn't come close to the higher ones like dogs. Aggression and team play were rewarded. Trying to capture the B flag at the start of the game was all out war. Most games of Domination were tightly contested. You weren't seeing 200-60 scores.
I really enjoyed BO3 though. MW3 was great for The Specialist Bonus and MOAB's. It's underrated but the camping, spawns, and lag were bad.