In team defender, if your team mate has the flag then you get double the points that you would get from a usual kill in most other game modes. If you have the flag then you get "team assists"(sadly they dont count towards killstreaks w/ Hardline Pro on.)which gain you 20+xp.

I use:

-PP90m1 suppressed w/ kick (But use which ever gun you are good with.)

-Stinger (To take down enemy killstreaks.)

-Semtex (I've played private matches, and it seems that a semtex is stronger than a frag against opponents with blast shield.)

-Trophy system [If you are to hold down a specific high traffic area (not camping)and an opponent brings in a killstreak with missiles, he would usually shoot at a high traffic area. So shove your TS down and it will block an incoming missile.]

-Blue Perk-
Extreme Conditioning (To get to enemies first.)
-Red Perk-
Hardline Pro (To get your killstreaks. And a 1 killstreak gains you ~250xp.Plus 2 assists count as a kill.)
-Yellow Perk-
]Marksman (For longer distances. You'll be able to see enemy gamertags above heads.

-Specialist-
2 Kills-(1)Recon Pro (If you are unable to finish off an enemy, Recon pro will allow enemies to see where your escapee has fled to and most likely take him out.)
4 Kills-(3) Dead Silence Pro (You will be able to sneak up on an enemy.)
6 Kills-(5) Recon Pro (All enemies will be louder when sound whoring.)

8 Kills-(7) All Specialist Perks (you will gain all perks)

25 Kills-(24) MOAB (kind of like a nuke. not sure really cause i haven't got one yet.)