You want the 2" drop hitch... where the lip is at the bottom of the square (2 inch drop) for normal utility trailers with 14 or 15 inch wheels/tires. Rented a 5x8 heavy duty solid wall trailer from Home Depot last weekend and it was perfect.
Even more drop (4 inch) is needed for the small trailer I own with 1 7/8 ball (4x6 ft) Lowes type utility trailer with 12 inch wheels/tires.
The 2" drop sounds right, that's what I use, my trailers all have the 15" wheels. Main thing here is that when the trailer is loaded and hitched to the vehicle it will be level to the ground, ie., not tipping to the rear or the front.