BS will always provide the most flexibility in it's bonus (pvp power, resil, whatever you want really), though in 5.2 JC is getting a couple hybrid serpent's eyes (
here), so their flexibility is improved in the PvP stats aspect at least, but BS still wins if you prefer to gem a secondary stat, or even hit/exp.
Eng will pretty much always be number one due to Synapse springs providing basically what amounts to any other professions combined bonus over the duration of 60 seconds condensed into a 10 second burst, which is very good for PvP. And after Eng, BS generally wins for the reasons above (not to mention BS bonus "scales" with epic gems, something other professions failed to do in Cataclysm 4.3).