Funnily enough, Sleepy Slumberland was my favourite, even though it was probably the only event where I didn't get the final dragon (had stuff going on and couldn't play as much as usual). But Knightmare is my absolutely favorite dragon as far as looks. I sometimes stop on him while cruising through my island and just stare. Honestly, I could have a poster of him on my wall. I think it's those pink eyes. (The dragon that I didn't get in that event was also a stunner, by the way, and I'm sad not to have him).
Also, at the risk of sounding like a broken record, I'd love Android players to get a chance at the events that took place before we could do them, particularly the space themed one.