Depends on what you feel you need. Rollins seems like a nice fit since you obviously need SB's, but I dont' think he'd win you the category alone so you would probably need to bring in at least one other SB guy along with him. Wilson is the best overall stat wise, so if you just to want to boost your stats in general he's the best choice. Cosby is the HR guy, he'll probably hurt your avg in the process but if you want a boost to HR and RBI he's probably the best.
Out of the 3 given your SB options elsewhere and Cosby's age, I'd probably stick wtih Wilson.