Miguel Olivo is also available as a backup catcher. Torrealba threw out 14% of baserunners last year. He's at 29% for his career. Olivo threw out 26% of baserunners last year. He's at 34% for his career. Offensively, they're about a wash. Although Olivo has a lot more power. Neither one of them is anything special, but given the choice I'd probably go after Olivo.
From a purely defensive standpoint, Henry Blanco is probably the best option out there, even though he's a dinosaur. Threw out 40% of baserunners last year. He's at 43% for his career.