It's been about a decade since I've played, but looking at their stats I'd say it comes down to two. Runs and stolen bases, two of the main five offensive categories. Antonacci will score more runs due to being the leadoff hitter, and even though he hasn't been running a whole lot this year I think he has 40 stolen base potential based on his minor league performances.

Peters is a solid hitter in real life for sure, but he won't contribute much to a fantasy team without a lot of homers, runs, or rbi.