I'd be a medic and start throwing med packs down. Then, lay down with the paddles out and just continue to fire them off. People will fall dead in front of you all the time and you'd be healing. You would reach lvl 100 in about an hour.
I'm pretty disappointed with the "expansions" overall. I think Close Quarters actually added the most to the game, as it added a completely different playstyle. Second would be Aftermath, as there are some pretty cool maps. So far not very impressed with Endgame, and I didn't even really play Armored Kill. Also, as far as I'm concerned, Back to Karkand is the base game, or at least it should have shipped that way.
I'll still probably pick this game up again, but it has lost some of its flair for me.
I've mostly played B2K, probably the best maps in the whole game(vanilla included). CQ is a close second. AK was a complete waste of time, aftermath is fun, but doesn't bring anything new to th game. Endgame was mostly worthless. Air sup. in particular.