Nico is easiest to write, because she's curious and not particularly shy about talking to people. Also because, if it's just her of the recurring characters, I can just write her in an utterly random place without having to worry about how it fits with worldbuilding on Eodea, or most other canon, because it can just have been "long ago".
I couldn't point to a single "least favourite" character, because, well... I write for fun. Writing characters I don't like to write is not fun, so I very rarely do it. :P
Possibly Ludovic in "Random Encounter".
... Though I am rather reluctant writing down most of what I have in mind for Daaren's and Sylvie's backgrounds due to worrying they're full of too much drama.