Very few of the CGs were our favorites and apparently most felt that way. They are basically stopovers and offer few amenities.
The best by far was Portage Valley RV park. They were very helpful, had a covered area for BBQ, fires and supplied the fire wood. Beautiful location, etc.
At Seward we got a WE site on the water which was great but no other amenities. We liked Deep Creek Beach which was dry but right on Cook Inlet. Alison Point in Valdez was dry and on the water. Most of the rigs in these locations and others preferred the commercial CGs.
CG's in the larger towns offer limited amenities. However they do offer location.
We made some reservations sometimes on the day of arrival. Anticipate ones that might be full and make a reservaion. Fairbanks and Homer were two for us although there were other options.
Primarily we planned to arrive at a CG by 1:00-2:00. To often many sites were reserved by caravans but this timing put us ahead of most of the rest of the pack for the remaining sites.
Be flexible and have backup plans. Or just pull off of the road as most of us have self contained RVs.