Hard to say.

Character - Arya - Her journey has been a nice slow burn. My favorite part thus far was skin changing with cats in her training. Excited to see her when training is done.
Place - Dorne - My favorite kingdom, and was really into Doran's plan with Arrianne all coming together.
Object - The Horn - If it comes to past and Euron does get a dragon that changes the whole dynamic.

My favourite is the one where Martin gets off his ass and finishes the books.

Dorne is so much more interesting in the books, the show has ruined that plotline by giving us only the Sand Snakes and removing Arianne and Quentyn.

Brans is the most mysterious and interesting, I just didn’t like the way they turned him into an Android. I really liked it when the Children of the forest were introduced.
I’ve enjoyed watching Arya grow into a silent assassin aswell, can’t really choose between the two in them.

Dragonsdragonsdragonsdragonsdragonsdragonsdragons

For me it's definitely Jon's and Tyrion's story line. For Tyrion I especially liked the slavery arc, he is now in a 'dark place' and I'm eagerly awaiting to see how this will unfold.
I’ve also enjoyed Danny's arc when she was presented to and then lived with Drogo.
But I was also really liked Dorne's story line, the sand snakes, Doran and prince Quentyn. Although understandable, it was a shame that their story line was really poorly presented on the tv show.

I'm most interested in Aegon & The Golden Company's campaign in the Stormlands.

I think they will take Storm's End and beat Mace Tyrell's army marching south which will give them the alliegence of most of the Stormlands. Then there are the "Friends in the Reach" that Peake spoke of and Arianne will probably pledge the support of Dorne to their cause (likely with a betrothal).

That will give Aegon a very strong army (Golden Company+Stormlands+Dorne+part of the Reach) and make him a very strong contender to the throne.

Yeah, the show went from a political war to a succession of sex and gruesome deaths only looking for the biggest buzz, forgetting completely any logic or political arguments. They skipped most of the "smaller" storylines and characters, which were making the interest and mystery of the books. Can't wait for the next book, I hope it will set things straight again.

I'm laughing (or crying) when I think about Disney hiring the series' writers for a Star Wars trilogy, and even more when I hear people saying that it's a great news. 

Yep, so many storylines skipped or altered in weird ways. Im a little worried for Winds since that last i heard GRRM is having a hard time keeping it one book.