They're very different styles of roller coaster. The closest thing to the Matterhorn at WDW is Space Mountain; the Florida version of SM uses a similar bobsled-style vehicle. Big Thunder has larger mine train-style vehicles that have you seated higher with two people side by side, which I think provides more feeling of stability. They're similarly wild, though. Big Thunder is much rougher (and I think more fun) in the back of the train than the front, and I believe it's a longer ride than the Matterhorn.