hare scrambles and GNCC are pretty much the same except hare scrambles is usually 2 hours and GNCC is 3 hours. If you get OLN TV channel, you can watch the GNCC races. They have a show on them.
I think hare and hound is out west style, someone help me on that. Around here, it is usually hare scramble or enduro.
Out west there is WORCS also.
You can go to
http://www.ama-cycle.org to find out more on each kind.
I have raced one AMA enduro and one AMA hare scramble. Both were SERA sponsored (Southern Enduro Riders Association). I liked the enduro better. On a hare scramble, it is a loop track, where it is maybe 8 or 10 miles for one lap. I had to pull over a lot on a little trail to let faster riders by over and over. In the enduro, it was one long trail and I started toward the rear. I never saw most fo the riders, and the few fast ones behind me only had to pass me once. Hare scramble is fast paced, but an enduro has some sections you can rest if you are "on time". I suggest you just try one of each of whatever is available in your area.