My best moments have been as a ground-pounder, although I occasionally pick up a jet/chopper/tank/APC. I especially like it when I manage to defend/contest flag points alone against lots of enemies. Two memorable ones-once as a commander in this one SF map, there was a side street sort of like ], with water to the right. I plopped down a supply crate next to myself, gave other ppl UAVs/arty and supplies when needed, and single-handedly fended off waves of armor (and occasionally got cartilleried, and sometimes temporarily lost the point). Also, on Warlord, I was insurgent, medic, at the TV station; defended it for a long time with the help of a couple team-mates. Truly, just a few people at that station, if they know what they're doing and have lots of claymores, can make it a PITA to capture (I remember some kills from taking enemy sniper kits and claymoring the stairs).
Also, I like it when I can get into a cohesive squad.