Barmes may get a shot to start at SS for the Rockies...in fact, he's viewed as a minor favorite. If he ends up starting, watch out...I'm of the opinion that he can hit in the high .200s, with homers in the high teens. The RBIs and Rs depend on where he'll bat in the lineup. He'd be a fairly good gamble in later rounds. I don't know long term...I mean, he's a good prospect, but Chris Nelson is probably seen as the future SS there...in three or four years.
Peralta broke out in a big way last season, but I'm really not sold. He's been pretty inconsistent year to year in the minors. Note that Brandon Phillips' year wasn't too shabby, either, so these two will compete for the job. Phillips was moved to 2B due to Vizquel being there, but could return to SS. Peralta's glove is better, though. Long-term, I don't see Peralta as a solution, although many scouts do. This year, if he wins the job, expect him to provide good pop for SS.
I'd rather have Clint Barmes, but that's just my opinion.