For the bigger rock rigs, Morris is probably better. A lot of hardcore trails, all very close to camp. Lots of good access trails so you can bring your girlfriends stock pathfinder in and park at the top to watch the show. However there is nothing really in between the two.
Choccolocco has a lot more trail riding. So if you have a rig like mine (nothing special, just a little bit of tire, a locker and some suspension), you can go out and play all day. I think it has about the same number of hardcore obstacle trails as MM, but you've gotta travel a ways to get to them. As mentioned earlier, lots of hillclimbs at Choccolocco.