It's personal preference. Executioner is a lot more burst damage, but depending upon how long you're in combat Savagery could be better (i.e. Executioner doesn't help much if it procs right when you get rooted or otherwise can't attack). Especially if it's not a great weapon, save some money and get Savagery.
Of course, if you do PvE with it too Executioner flat-out destroys Savagery, but in PvP it's a toss-up.