There are so many characters in the show, but my top favorite is Varian. I actually have a reason for this.
1: He is a smart boy, and he always knows what's going on. He is very intelligent for a 15 year old boy and even built a working robot :D
2: He's adorable. I feel like the writers did this on purpose so that everyone can love him. I'm pretty sure he knows he is as well.
3: He is understanding. In "Cassandra's Revenge", he understood her path to darkness, but told Cass that it is a bad feeling and that she should turn around into lightness.
4: Understandable in general. I think we can all understand why he went into evil in the first place. We understand that he wants to get on the "Right side of history." in "Rapunzel's Return."
There are many reasons, but these are my main reasons.