Depends upon your tow vehicle. I think the general consensus is to tow as level as possible to keep weight distributed evenly between the axles. You can buy ball mounts of varying drops/rises for your specific application.
I have one that will adjust to 3 or 4 positions. But I hate it because it seems to shuck back and forth too much for my liking.
I have a CAM Superline 6x12 low profile with ramps & tarp, 11,960 GVWR on order myself. Can't wait til the end of the month when it arrives.