At first, this appears to be nothing more than a preference trade. The combination of players is fairly even.
However, if it's a keeper league, you definitely want Kemp/Aybar since Kemp is the best keeper in the deal. Unless the number of keepers are high or the league has 12+ members, you won't be keeping the SS anyway.
If it's NOT a keeoer league, Kemp and Aybar give you more SBs (and maybe BA) and Bruce/Cabrera give you more HRs. I'd say the SB/BA angle is more reliable, but it depends on what you need. I'd take Kemp.