Jhonny Peralta doesn't have the best range at shortstop and would arguably benefit from a move to third base. But he has very solid hands and fields the balls that he can get to very well.
In 2011, Peralta handled 608 total chances at shortstop and had only seven errors, for a .988 fielding percentage. He had the third-best fielding percentage in the majors and was tied for the third-lowest number of errors amongst shortstops.
Last season, Peralta handled 595 chances and once again had only seven errors for a great .988 fielding percentage. Peralta's numbers were good enough for the second-best fielding percentage in the majors to go along with the second-fewest errors among shortstops.
While Peralta had a good statistical season, he lacked range. That is where J.J. Hardy is exceptionally better than Peralta.
Hardy has amazing range and can get to ground balls deep in the hole. Hardy is very adept at turning the double play and, like Peralta, has great hands.
Hardy was always a very good defensive shortstop, but he has really taken it to the next level in his two seasons in Baltimore. As he matures, he has learned to position himself to better handle more ground balls.
Hardy played very well in 2011, with only six errors to go along with a .990 fielding percentage on 620 total chances. Hardy was second in fielding percentage for all shortstops and tied for fewest errors at six.
2012 turned out to be an exceptional year defensively for Hardy, and it ended with him receiving his first Gold Glove. Hardy was nearly flawless with an amazing .992 fielding percentage. While he still had six errors, he handled a whopping 779 chances. Hardy had the best fielding percentage among all shortstops and also had the fewest errors.
Hardy showed no sign of slowing down, so there should be no defensive letdown in 2013.
Advantage: Hardy by a large margin.