This is going to sound like a cop-out, but it's true. I like the variety. Indeed, one of the perks of being a media tie-in writer is that I get to stretch my muscles by writing in lots of different genres: sf, fantasy, horror, murder mysteries, spy thrillers, kid's books, even at least one historical romance. I like to think it keeps things fresh and interesting! I'm a modern-day pulp writer at heart. And a jack-of-all-genres. Movie novelizations are probably the easiest to write, since the screenwriter has already done most of the heavy lifting in terms of the plotting and dialogue, but even those can pose challenges when it comes to trying to visualize a movie you haven't seen yet! As for writing for fun? Do social-media posts count?