I actually had to think pretty hard about this one, but I went with Groove Tube in the end. It was really a toss up, since both have such strong skits and some weaker skits. The Tunnevision theme almost had me on "their" side. It gets stuck in my head for days on end if I watch it. I tracked down a 7" radio-promo EP for Tunnelvision, just so I could have a good recording of the song. I wonder if one exists for The Groove Tube.
Also, what other films are there like this? I know of The Boob Tube, Sex O'Clock News (which is This is America/Jabberwalk clips...and I'm guessing clips from other films as well spliced together), American Ticker with Joe Piscopo (which I haven't seen, but recently picked up a $1 VHS at a flea market), Amazon Women on the Moon....and that's all I can think of off the top of my head. I do really like some of the video release things like this...particularily Mr. Mike's Mondo Video. I also just borrowed a copy of Mutant Video with Jim Belushi from a friend, but have yet ot watch it.