Well, I can certainly recommend RBL:Protected Sky - Yellow. Not a single false positive in the past week and they have routinely caught Spam no one else did. In the week that we used this it was the 5th most effective RBL (behind SORBS - Recent, UBL, UCEPROTECT L1, and BACKSCATTER). They were slightly more effective than GBUDB.
Effective Rate: Overall, 2.5% of all incoming email were caught by Protected Sky - Yellow with 0 False Positives. This RBL was responsible for 11% of all incoming messages flagged as Spam with 0 False Positives.
As far as RBL:Protected Sky - Red we didn't have a single hit in the past week. We are probably going to disable this one as it seems to have IPs listed that we probably already have blocked with SmarterMail's Blacklist (although Y.M.M.V. if you don't maintain a large Blacklist in SmarterMail).