I tend to worry when people need to use elaborate half pads, because it can compromise a well-fitting saddle, or attempt to compensate for an ill-fitting saddle. If your saddle fits your horses back correctly, then a sheepskin pad should do the trick, just to smooth out any less than perfect spots, and make everything look a little more put together.
As it has been discussed here already, I won't go into it too much, but memory foam pads compress when you sit on them, so they can be really tricky to work with when tacking up. I've had a lot of problems with them causing my saddle to move, or making sure my girth is tight enough after mounting.
I don't jump, but in general I prefer sheepskin to memory foam. I think it better distributes both weight and impact on their backs. While over padding can screw up the fit of any well fitting saddle, I find memory foam pads to be difficult to get the fit right with the saddle even though it "compresses."
I prefer an fuzzy sheepskin half pad. It provides maximum comfort under the saddle, and exceptional benefits for both horse and rider, helping to reduce rider movement, protecting the horses back, and creating a better saddle fit. Increases performance in how horses lift their backs, and all riders will sit closer, quieter, and be able to do more with lighter aids!