Of the current arcs the story is on is Punk Hazard (we're barely three chapters into Dressrosa so I'm not counting that yet) and the ever epic Trafalgar Law, new fan favorite.
There are obvious reasons for his popularity; his character design is just wonderful, and let's admit it- he's just...pretty.
He has those things that make us interested in him; he's smart, ruthless, a planner, snarky, proud and we don't know what side he falls on. He has been described as a cruel, ruthless pirate of the One Piece world and he is. However, he's shown a surprisingly lenient side for a cutthroat war lord. His tolerance of Luffy (and the fact he saved him for no apparent reason), his warning to everyone that Punk Hazard would be flooded by poisonous gas and anyone left behind would die and in recent chapters his increasing show of his humanity - the first we've seen since the Punk Hazard arc. Surrounded by the influence of Luffy and the Strawhats he's acting like a normal human being. Oda, as always, has managed to create a well rounded interesting character. I want to know more about Trafalgar Law and am super happy that he seems to be appearing within the next two arcs, at least. We may even eventually get a back story for him.
What makes me really, REALLY happy is the fact that his popularity means massive fan works by amazing artists. These are all yanked from Pivix (and credit goes to the artists which I would have posted but I can't translate Japanese so...) That is my recent obsession.