You should definitely go for lord of flames (burning hunger mostly) and impish incineration first (you should play sac vs a lot of cleaves where interrupt isn't important). Then depending if you're going to play a comp where you can utilize chaos bolt spam, or a high dmg pressure comp (feral/destro?), you're going to either go down for chaos bolt dmg or up for more immolate+conflag dmg. Personally I'd skip dimensional ripper if you're only planning to pvp as destro, you will almost never cast incinerate in arena.
At the end of the day it doesn't matter much, slightly more immolate/conflag dmg, or a decent boost to chaos bolt. If you are scarce on artifact power, I would probably just go lord of flames+impish incineration and then straight for -30sec cd on unending resolve, and then continue from there, depending on which playstyle (cremation or focused chaos) works the best for my comp.
Remember to suicide off a flying mount after every arena to reset lord of flames cd ))))))))))))))))))