The impossible question.
PoE is a "better" game and is still growing. It's hard to get into at first but it's really rewarding to get far in it. Early on it feels clunky but after you get more movement speed and your build comes together it flows really well. The trade system in PoE is complicated (but has gotten much better from what it was).
PoE is free, but if you plan on playing it for a long period you MUST buy stash tabs. I recommend to buy packs which include both skins and currency. You get the skins for "free" and use the currency to buy stash tabs.
Diablo 3 is much easier to get into. As long as you're not top pushing for top 5 on leaderboards the game is fluid and fun to play. You can't go "wrong" when playing the game since you just change spec/gear and go again.
My experience of the games comes from playing HC. If you die in PoE you are punished much harder than in D3. You have to start over except for the things you had in your stash but in D3 if you die, but you keep your Paragon levels which is really strong to have to start over and you just get someone to boost you to max level again in 5 minutes. But you still loose all your gear, gems and augments.
I hate SC Diablo, but I would be able to play SC PoE since the game offers some fun and hard challenges.
