I too usually prefer state and national parks, but do use KOAs during long travel days as they are generally clean. Haven't stopped at one yet I passed on, but have driven by some I wouldn't stop at.
Funny story is on our last trip out west in 2005, we started to stay at a state park in Minnesota. Fee was going to be $25 for the night, $10 for the vehicle pass, and $6 for the two kids. Though the fee was outrageous, we were tired and wanted to stop so agreed. Then they wanted the kids names and we both were like why since they were only 14 and 12 at the time. Giving their names is a safety no-no. So we decided to move along. About an hour down the road, we found a wonderful little KOA out in the country. Owners were the only employees, great folks. Price was much less than the state park, they let the pool stay open a little late for the kids to enjoy a swim, and it was the cleanest, nicest little place we ever stayed in.