I don't necessarily have a least favorite genre, but there are a few of them that I wholly suck writing for and it's why I choose not to do them. But, for the sake of doing it in order of how the question was written, I shall list my top three favorite genres to write for:

[color=39b54a]✔ High School Slice of Life
✔ Urban Fantasy 
✔ Small Town Superhero mysteries[/color]

I feel like these three could be combined into one unique rp, but even when separate, I really enjoy writing these three genres because, a, it doesn't take [i]much[/i] thought from me in the sense that I would be able to focus more on the plotting of character connections. Plus, when it comes down to it, I have more of an investment in these three genres than I do in the next three that I am about to list.

[color=ed1c24]✘ Medieval Fantasy
✘ Sci-Fi
✘ Horror[/color]

Again, these aren't three genres that I don't like. I mean, I adore all three genres, but I completely suck at writing in these kinds of settings. I don't know if it's because I have little experience and I don't put myself out there or what. All I know is that my writing style is more in line for modern settings because I enjoy throwing in pop culture references into my writing and it's better to use them in a time where they are relevant than -- well when not. Also Horror and me just never have clicked writing-wise because I suck at using the right descriptors I would need to build suspense.