Site-specific Ressies or whatever's available? Preference?

Va state parks have the same system. They guarantee you a site that fits your RV but not a specific site. So far this system works for me. As long as I know I have a reserved spot that fits my rig I'm OK.
This keeps the same people from locking down the same sites every year. It keeps the sites circulating in a random order for the most part.
In the end it's the luck of the draw for everyone which is seems fair to me.