Reverse sidecut skis(I count ARGs as reverse, 1mm isn't going to drag and the flat spot adds stability in pow actually) will be much 'better' than skis with lots of sidecut in pow. JJs have like a 14m turn radius or something tiny like that, so they have A LOT of sidecut over at least 1/2 the ski.
By 'better', I mean you can smear them super well and they aren't hooky. Some people like hooked in turns in pow, and with the JJs taper that will be easy. So both will be good, but my preferance would be ARGs(not to mention landing cliffs with the bigger waist is nice). The JJs also have plenty of camber, which(based on how Chetlers skied) will make them super poppy turn to turn in pow, but will also dig the tips in a bit, so even more locked in feeling(although getting out of turns isn't going to be hard like it can be in pow on park skis).