Fantasy is definitely my favourite. I'm old and have read and watched a lot of movies, and the other genres, at least in their pure forms just don't vary between each other as much as fantasy does. With fantasy you get to travel to an entirely new world and see different magics, beings and places. I mean, you can write whatever you want, why not an entire new place or types of beings?
Thriller/Mystery can be absolutely fantastic, but it's usually difficult to pull off and good examples of them are few and far between, with most writers not being able to pull them off competently.
Action is boring by itself, unless the fights are strategic. Otherwise they're pretty boring, it needs to be mixed with other genres in order for it to be good IMO.
Sci-fi is a funny one. It's like fantasy, but seems to be more restrictive and needs to be bound to the real world. Also it becomes dated more quickly. Can be cool, but it seems to be hard to pull off, and I like it less overall than fantasy.
Slice of Life is bad IMO, especially pure slice of life like KON. Mixed with comedy it can be good, but otherwise, meh... I haven't really given this genre much of a chance though I admit.
Romance is undoubtably the worst though (no offense to anyone who enjoys it of course). At worst, it devolves into pron and someones fetishes, but even at it's best, it's very predictable and is pretty much just wish fulfilment, doesn't really challenge you at all, and is never really that realistic either. It can be nice, but more often than not, the stories never really stay with me.
