None. Shooting is too over used nowadays. I'd rather have a minigame where you have to escape stuff while being timed or challenge in a rocket ship. More Shooting or Racing for GTA Online 2?
Have a NVZN-like minigame (shoot aliens, get guns, some simplistic thing to pass time)
Have a minigame where you have to destroy the most amount of property on a limit of time (basically, GTA in a nutshell)
1st option sounds like Destiny or Halo. 2nd option sounds like Tetris or Duke Nukem