AK Fest is May 1st & 2nd. I would avoid that weekend. May 9th is Mother's Day. The long weekend of May 28-31 is Memorial Day weekend. The weekends of May 14-16 and 21-23 appear to be conflict-free.
I know that the last two weeks of May are crazy for us with two kids in school. I don't know if this affects many others as I'm definitely at the younger end of the spectrum of attendees
I've heard both sides of the kids in school situation. Many don't want to waste any possible family vacation time to go to the fest after school lets out (although in my mind we're only talking a day or three at most--not really long enough for a proper vacation IMO), but others like myself can't really get away those last two weeks of May.