Brian Roberts' starting stint might be in question when Jerry Hairston, Jr. gets back from the DL. He was sidelined with a fractured finger and has been sent to the minors for a rehab stint. I don't think the O's are in any hurry to rush him back but they might trade either Hairston or Roberts depending on which one is having the better season. Hairston might have the upperhand in that regard. Roberts wasn't a prolific base stealer by anymeans in the minors and was kind of a surprise last season. Hairston, on the other hand, was leading the league in steals last year when he went out. He might be an injury problem though.
If you have to choose between those three I say definitely go with Dave Roberts. He plays almost everyday, and anytime he is on base he has the greenlight. He has a very high OBP as well which will help him get a lot more steals.