Hardpoint or League Play are probably best for points. Hardpoint has the highest SPM of any game mode and League Play is 7,500xp for a loss and 10,000 for a win. Run UAV, Counter UAV and VSAT (obviously not in league, lol) and bring a couple of EMP grenades for extra points from team mates too.
Search and Destroy. The games are fast and give you 5x XP per kill. So lest say you get 5 kills in a match that is same as 25 kills in other modes. And you add to that also the other bonuses and you will level up pretty fast.