Round - Round lipped wheels are what you see on normal skateboards. The “edge” of the wheel is rounded, which provides less traction through turns. This means that they are easier to slide on than the square type, making them the clear choice for freeriders and freestylers. If you are new to longboarding or want to bomb hills and rail corners as fast as possible, look into square lipped wheels.
Square - Square lipped wheels are the typical longboard wheel shape. Instead of the “edge” of the wheel being rounded, it’s, yes, square (at a 90° angle). This provides better contact with the road, which in turn provides much more traction and sliding resistance. Square wheels can still slide once broken in, making them excellent for downhill and cruising/carving.