Bark

Pros: Makes for tougher plants. Reduced risk of overwatering. Easier to see state of roots.

Cons: Needs watering more often. Harder to tell if it is wet enough.

Moss

Pros: Plants grow larger. Looks attractive. Surface lightens when it dries out.

Cons: More prone to waterlogging. Risk of compacting when repotting. Slight risk of skin disease from moss-borne fungus; wear rubber gloves when handling.