I think, to do each genre justice, that each would need its own book. To me, having a mix is okay, but I like the idea of really being able to advertise Fantasy or Sci-Fi and come through with the goods.
Plus, I really enjoy what modern writers and filmmakers are doing to bring new aspects to the genres and I'll really be looking to reflect that.
Modern films like Avatar, District 9 and Prometheus present cool scenarios in which a Sci-Fi monster hunt could take place.
Superhero movies and graphic novels are at a high point, which is very inspiring to the creation of monster hunting heroes.
Fantasy is probably best represented by Tolkien and Martin right now - plenty of inspiration there.
YA is probably the fastest growing genre at the moment, and keep in mind that YA does not imply childish situations - it only demands younger characters and their POV. A hard-bitten monster hunter with experience is one thing - a sixteen year old facing their first hunt is quite another.
And then there are the genres that have been overlooked for a while. An Occult Detective volume is my personal favorite for this category.
John is right in that everyone can rally behind a monster hunt - that's a big part of what has inspired me over the years. Now I want to explore what kind of great stories are out there in writer's imaginations!