The big differences:
On the Beach, is very small, tight spaces, in town, sand and gravel drives and parking. It's just a 1/2 block behind the dune to the drivable beach.
Pioneer, is huge, maybe 4 miles south of town, long boardwalk to the beach, up to maybe a 1/2 mile walk if you are on the west side of the park. But all paved concrete pads and drives, and better parking. The town shuttle comes down to the park, to do their turn around and head north. Also I think I read, you can not drive a rental golf cart in the park, and carts are rented everywhere for driving town and the beach.
Don't miss the Belt Sander Races at the Gaff on every other Sat. Get the local tourist paper, and buy a Port Aransas Beach parking sticker for $12 to park on the beach.
Dave and Dolly
1998, 36' Foretravel, U295, rare mid door
2001 Jeep Grand Cherokee