I've been describing my superhero novel--well, it's more of a deconstruction of superhero stories--as urban fantasy because there was originally no scientific explanation for the sudden development of increased psychic ability (read: superpowers) in humans. But in the most recent draft, scientists are studying increased psychic ability and are making progress (for instance, one researcher figures out what predisposes people to increased psychic ability), so that rings more sci-fi to me. The story is also about an anti-hero who uncovers a conspiracy to kill hundreds of people and blame it on exposure to psychic power, so there's a race-against-time element as the main character tries to take down the conspiracy. Would that make it a thriller? I've never had so much trouble putting a genre label on a story before, and I can't very well go looking for an agent if I don't know what genre my own damn story is.
I think "superhero novels" are simply starting to become its own thing now. You have stuff like Brandon Sanderson's The Reckoners, April Daniel's Dreadnought, etc. I've seen people run into similar problems as the ones you demonstrate in your post in trying to define these works on the basis of the more established novel genres. If that's not an option as a description, I would go for the genre that sounds like it would be least likely to disappoint people. For example I imagine a thriller reader coming off from their Jo Nesbos and Robert Ludlums spitting up their coffee the moment someone tried to bend a fork with their mind. Unless it's a gritty "deconstruction" where every strange phenomena is explained by science, even if you don't go into technical details, "urban fantasy" would probably be your best bet. Otherwise you could maybe call it a "science-fiction thiller" or something, "thriller" to show it's still sort of grounded in a modern setting? Okay, I don't know either, lol.
I would consider it fantasy, though the publisher ultimately decides what the book is categorized as.
I was thinking the same thing as @SadStories - I feel like there are enough Superhero stories out there that you could probably use that as a sufficient description when contacting agents.
