Hardpoint and Headquarters play the objective as much as possible while getting as many kills as possible. Also another good idea is to have the FIM-92 Stinger on and take out kill streaks because people use UAV's and Care Packages alot so that'll give you some more xp and FIM-92 Stinger challenges and cameos which give more xp challenges

The #1 most XP-Rich game type is by far, in most people's opinion, Kill Comfirmed! However if you have Nuketown there is a lot of XP in that as well.

I would have to say Hardpoint you get so much xp from that gamemode if your inside the hardpoint with it captured you get +200 plus +150 xp for every kill while you have the hardpoint secured

If you have the Nuketown 2025 map then that would be your best bet for the most XP.

If not then Kill Confirmed is good because you get 50XP per kill and 100XP per dog tag collected. You get 25XP if your teammate collects your dog tags. Hardpoint is also good for XP.