1) Jaime Lannister. The best character arc in the series. Towards the end, I got the sense, that why he did some very bad things, he was easily one of themost honourable men in the whole series despite being a 'bad guy'.
2) Arya Stark. A very developed character, who has been consistently one of my favourites in the show. Basically goes from a child to a fully realised D&D character by the end of it. Now she is regaining her humainity, easily 2nd place.
3) Jorah Mormont. Good old, Jorah, blindfully honourable and stillan ex slaver and a betrayer initially of Dany. Like the two above, a talented actor, who showcases a lot of emotion, I beleive in his character and has some good action scenes.
4) Tywin Lannister.You honestly beleived that this guy was the most powerful and probably the most intelligent and driven character in the realm. His scenes with Arya fully showed the depth of his character as being someone who probably would have loved ot have been a good parent, if he wasnt so scared of becoming like his own father. Limited time in the series, but he made an impact.
5th place could be either Dany or Sansa. Sansa is a stronger character now, whilst Dany is largely built by her relationships with the dragons.
10) Euron. He's not a character. He's an oddity. Walder Frey, Ramsay Bolton, Joffrey - made me feel something. Euron just wanted me to have his scene over with.
For a top four its hard not to go straight Lannister. They are all excellent actors playing nuanced character and were well written. Tywin, Tyrion, Cersei and Jaimie.