Possibly, averaging things out over the years, Glastonbury. Ample folk music, and of course ample every other kind of music to compare and contrast. And, surprisingly enough, absolutely excellent sessions, proper jobs, round campfires, till dawn and beyond. And certainly plenty of stuff for widely varying age groups.
The buzz of seeing super-stars, if that is your thing; or the thrill of serendipitous wandering and seeing what is going on in obscure strange lurking yurts that you can never find when you go to have a look the next night.
    All that, plus the virtual certainty of running into someone you haven't seen for years.