Sabin, because a cage match is a wrestling match first and foremost. I'm pretty sure magic is against the rules in such things.

Terra would be in the 'slumped on the floor but holding her torso up with her hands' pose, Cyan would be in his 'gotta protect thou lady' pose, Shadow would put up a good fight due to his quickness and Umaro due to his strength, but in the end Cyan would carry Terra away from the cage and get counted out because he doesn't wanna hurt nobody, Umaro would fall hard at some point, Shadow couldn't manage without his weaponary. Sabin, though. He's a mean, lean wrestling machine.

Saying Terra could beat Sabin in a cage match is like saying Sabin could beat Terra in a wand fight.