From what I've seen, the majority of agents (at least those who represent graphic novels) represent both adult and YA. If they
only do YA, it's because they specialize in children's books/MG. The only other one I see on my list that wants just YA/younger GNs is Rosemary Stimola, despite representing some adult fiction.
Veritas Literary Agency doesn't seem to express any interest in YA, and neither does Rob McQuilkin of Lippincott Massie McQuilkin. Same with Samantha Haywood of the Transatlantic Literary Agency.
The Susan Rabiner Literary Agency represents primarily "narrative nonfiction", so you may not want to bother if yours is fiction.
Others, like Evan Goldfried, say they are specifically interested writer/artists, not just scripts.
I'm sure there are more, but those are just the ones I see at a glance. The overarching thing I see is a lack of interest in superhero-themes. YA is probably an easier sell, because of the manga boom, but strong literary works are also a draw (because of the success of Persepolis, Fun Home, etc). Adult "genre" fiction is most likely toughest to sell, but that's just a feeling I get...
Feel free to post how long your query responses take, you guys! If anyone wants to know how long my turn-around was for any agent in particular, just ask.