I have yet to watch the third, but I'm eager to see it! Sometimes one begins to get paranoid that the crescendo of a trilogy is going to be lazy and slapdash because the creators were overconfident or bored of it, or something, or just looking to take the money and run. Why does The Hobbit leap so mysteriously to the synapses? Hrmm, hrmm, hrmm... but HTTYD is a labour of love, definitely, and it's great that the third movie has met the same standard of quality as its predecessors. Or reputedly. Still have to watch the dang thing.
Hiccup is my favourite character, by far. I relate to him a lot, bravery and spike in competence excepted. He's flipping endearing for the whole ride. My favourite dragon is either Hookfang or Toothless, but the Cloudjumper that Valka rides is a definite competitor.
I've read about three of the books, which were hilarious and genuinely entertaining, but it's an electronic nightmare trying to get more. I totally recommend them. They're very different from the movies, if not completely, though just as fun. The prose is very childish, though. Scholars might be put off. And I've watched a couple of episodes of Riders of Berk. The series is not the prettiest thing to behold, but its still good.