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

Around here, we don't have that problem. There are very few reservable sites in State Parks or USFS campgrounds; at least, the ones we are likely to use. Some USFS campgrounds have reservable GROUP sites, but individual sites are mostly "First Come, First Served", and if you pay for a site you must occupy that site the first night.
Of course, there are exceptions, as always.