Simple answer, neither, they both do different things and they both do it well. Check out screenshots and read a few reviews to see which suits you best.
However to be a bit helpful from Buy POE Items
playing a lot of Diablo and researching Path of Exile's. I will break down some of the differences.
Diablo 3 lets you play with a variety of skills that get augmented by 6ish runes per skill. Swapping skills is super easy and it allows you to play around with your play style on the fly. Potions are also different as Diablo uses them to recover for a mistake rather then being a part of you're health pool.
Path of exile has a complex skill tree which changes the way you can play you're character, you get skills from the gems you equip in POE Trade Currency
you're armor and you are more so "Building" you're character as you level through the skill tree. Potions play a bigger role and are important, I don't know too much about them but if you want to do more research the skill tree and potions would be a good place to start.
You could also check out Torchlight 2 which sort of has a middle ground between them.