Depends on how much trouble I was in.
If I was in really big trouble, like say, out of ammo with the enemy on all sides, than I would pick Superman since he is bulletproof and could extract me all by himself.
If I was in little trouble, like alone on a city street facing the local gangbangers, I would take Batman, since I could knock a few heads myself and then get a ride in the batmobile with the hope that I might get to drive.