There are 4 levels of sites. Partial, Preferred, Full, and Premium.
Partial is not part of this discussion. Loops 1500 and 2000.
Preferred and Full offer the same facilities/amenities the only difference being LOCATION. Preferred loops are loops 100, 200, 300 down close to Pioneer Hall, Trails End, and the marina. Full loops are loops 1600, 1700, 1800, 1900 and are further away from Pioneer Hall, Trails End, and the marina.
Both Preferred and Full have a concrete driveway with a sand pad at the back of it (also called a coquina pad because technically it is made of crushed shells not sand but you get the idea). They both have cable, water, power, and sewer hookups with a basic picnic table and grill.
Premiums are all concrete (no sand/coquina) and have oversize concrete pads with widers turnouts to make it easier to back in big rigs. It has a square picnic table and covered grill (different from the non-Premiums). Of course it has cable, water, power, and sewer also. They are all over the central part of the Fort and are the majority of sites available.
So the difference (to answer your original question) between Premium and Preferred is both location AND amenities. Ameneties being all concrete, upgraded picnic tables and upgraded grills. So it's a little bit of apples vs. oranges in terms of a comparison. But I hope this helps you make a decision about what type to get.
Good luck!
Bama ED