I'd have to say my strongest writing is in analytical or criticism. It's what I have the most experience in and what I enjoy the most. I have a hard time with fiction; over-thinking, questioning everything, you know.
I think my strongest would be fiction. It's just what feels most natural for me and what I have the most fun with. My weakest is most definitely poetry. Whenever I had to write it for workshop, it just never sounded right. I feel like my brain just doesn't work like that. I think the question of whether or not a genre comes naturally to someone is a super interesting one. On one hand, I want to say no, that you could get good at anything with enough practice. But on the other hand, I think of my aforementioned relationship with poetry and am inclined to say there are some things you either have or you don't. It might just depend on the person?
I am best in fiction and pretty good in poetry, though I'm not as great with sci-fi or fantasy (primarily the world-building gets me in those ones). I think practice always makes writing a certain way or in a certain genre easier, though people may be better at one over another because they like that particular kind of writing, which then likely helps with the writing process for those works.
I think you should you should write stories similar to the stories you like to read. They seem to give me the most inspiration. Fiction Thrillers are my favorite.
My weakest would most definitely be non-fiction. From my toddler years all the way to now, I've always been submerged in the world of fiction and have surrounded my writing in it as well. I think since I don't read non-fiction that often, I don't have a sense of even how to structure my writing in that category.
I enjoy writing thriller fiction and find whatever I'm reading will emulate my writing.