It depends, Kill Confirmed is probably the best if you are good at it. For me though I can get more XP in FFA because I'm better at that mode and can come in first a lot. Also try using Scavenger and Hardline. Everytime you run over a dead guy your Scavenger will give you XP and every 2 assist counts towards your killstreaks which also helps boost the XP you get in a match. Good luck man.

Kill confirmed and FFA for sure.

http://www.youtube.com/watch?v=L_V2a2-JEQQ

http://www.youtube.com/watch?v=zIv5KNlJqVE  This one is better.

DROP ZONE!!!!

The most important thing is definitely use specialist. Huge experience unless you consistently get killstreaks to get to high assault streaks, but even then specialist might still get more experience.

Support has some good options, recon drone is sweet exp on most maps, ballistic vests can shell some decent exp depending on the team, EMP can be good if you destroy a lot of enemy equipment and aircraft, etc.

For modes I would probably say KC if you like to gather tags (especially your own), or dom. Drop Zone is HORRIBLE, don't do it.

Kill Confirmed on a double XP weekend.  And don't grab your own kill tags, let your team-mates get them (and vice-versa) to share the points.

Or... DZ if you shoot down choppers, killstreaks, etc., and also Recon Drone in DZ during double XP weekends.  There are always Recon drones in DZ, many players simply leave them behind.

I used a prestige token during double XP weekend and was running Quad XP.

200 for every Recon Drone tag, 160 for every assist.   You can really rack some points up with that on certain maps and with good team-mates who kill quickly.

Like on Dome... had a 23 assist game last night because I was just trolling the other team with the Recone Drone.  Hover it in the middle of the map up high, and just spin it around and tag people just about anywhere in the map.  If they are inside the building/dome/tunnel.. they won't be there for long.

When I prestige, I play KC with Specialist so I can run Challenges concurrently in addition to in-game XP. I'll switch up the Specialist load outs as they get completed.