The barrett for sentimental reasons :-)
also I think the setup for assault rifles in mw2 were awesome, guns with the same feel as them would be good. I hope no shit from blackops gets on, apart from maybe combat training (with prestiging). There also needs to be 2 or 3 3 burst weapons. I would also like a good weapon order - best gun last unlocked. not like black ops (by level 17 you've already unlocked the god guns - famas and ak74u) and mw2 (ump)
I think camos should return, and the system for earning them by headshots. by taking away the challenges to earn camos and attachments kind of took away the rewards for using a gun. to me black ops was shit as there was nothing to do apart after you've got to 15th level 50. the whole game is just leveling up.