I looked at both, and then some...
...before I bought my Catalina 36. Nothing against Hunter, I seriously looked at a H35. The right boat presented itself at the right time, at the right price. Hunters and Catalinas, although similar in construction as LaDonna says, seem to have a difference character. Hunters are big on innovation and new styles (there are a bazzilion Hunter models that change every few years) whereas Catalinas stick with what works... there are positives to both approaches. The Hunter B&R rig is a pretty cool innovation (let's not start that debate about the arches) and those Hunters sure know how to use space (check out those overhang decks). They also sail very well, especially in light air. The Catalinas look a little more traditional (still not much teak) in their lines (some say boring?), and the company likely still procuces parts for your 15+ boat. I surmise that there are so many Hunter and Catalina sailboats out there because owners of both are loyal. I started as a sailboat "snob" and have learned to respect both manufacterers as companies that are still in business "after all these years..."!