most coloration: rainbow darter
most aggressive feeder: pike or musky
most unique look: sturgeon or burbot
most easy to breed: sunfish (most species you can breed in a rain barrel)
most scientific study: stickleback
most rare: hells hole pupfish
Just a few ideas of mine. Most awesome is a tough category. I'd say one of my favorite to keep are green sunfish, they get very personable and easy to keep. However, they are hardly unique. Their ubiquitous nature seems to make them less appealing for some reason.