Ditto what RayP said. I've been using circle hooks for a long time. The secret is to let the catfish take the bait and not to jerk your line too soon. They'll hook themselves.
I prefer Gamakatsu in 6/0 or larger.
Gama's are great circle hooks. I don't catfish but they are the best for snapper fishing. Tyme is right, all you gotta do it start reeling. Teaching yourself not to set the hook is the hardest part about using them.