I enjoy writing humorous/funny characters a lot, but I sometimes also like writing more bitter or angsty characters, too. It depends on my mood, I guess.
I prefer writing characters with a sense of humor. Humor has always been an important part of my life and its easier for me to write characters that make jokes than those who are completely serious.
I really like writing contrasting characters. By this, I mean I really like writing stories from multiple perspectives, and then having their views and thoughts clash with one another. I don't do it too often, but it's tons of fun. As for individual characters, I'm not too picky. I suppose I do like writing cynical characters the most since they seem to always have something to think about or an opinion to weave into a description. I find them a lot easier to write than optimists, at least.