Love Spinal Tap, that's the best. That was my life back in the 60's - 70s', welcome to way-down-from-top-level rock 'n roll. They really nailed it.
Best In Show. So-so the first time, gets better with repeated watching (my 13-yr-old son loves watching stupid comedies over and over). Great movie.
Waiting for Guffman. Not as good, and not as good repeated watching.
Mighty Wind. Not the absolute best, but some amazing moments. Thorazine man! And the guy pointing up to the ceiling and saying, hey, there are lights up there. I've only seen it 5 or 6 times so I don't have it memorized yet.
As the old saying goes - if you like that kind of thing, it's the kind of thing you'll like.