Sockets don't work in arena, and strength is better than mastery since the 4p PvE tier has no influence in PvP.
Roughly, str > crit = mastery > versa = multi.
Sockets didn't work in Arena because there was no socketed PvP gear and didn't want PvE gear to be an advantage. Once they added sockets on PvP gear it now works in Arena. It's PvP gear of course the sockets work now.