The only 2 Zappa albums i have are The best band you never heard in your life, and Tinseltown Rebellion which i haven't seen mentioned here. I really like them both, but how do they compare with some of his other highly rated material?
I consider them both "later" Zappa, which isn't necessarily bad, but it has a different vibe. Early Mothers stuff was so unstructured that a lot of it seems pretty pointless to me. Yes, I understand what they were going for, but heck, my friends and I also recorded ourselves fucking around for a few hours with various pieces of musical equipment; that doesn't make it art.
By the early 70's, however, he'd definitely found his voice and I like just about everything from that period. He was stretching out as a composer and had learned some things about arrangement. It's interesting to me listening to those early "orchestral" works being performed by the what he had available to him at the time: rock ensembles. But he was also at his most creative in terms of just plain insanely funny songs and stage shows. The Flo & Eddie years, the Roxy & Elsewhere band. Those are the shows that inspired the phrase "You can't do that on stage anymore".
I have the two you mention, and they're both great. The demented cover of "Stairway to Heaven" is awesome! But you can almost hear how Frank had started to get a bit bored with the format by then. He was skewering a lot of topics seemingly just because he could, getting a bit political and downright cynical, and it reminds me a bit of what happened to George Carlin towards the end. He went from funny, to funny and cynical, to just bitchy and not really very funny anymore. Frank was still pretty funny in the 80's, but this is some of the last stuff he did before he retired from live performance and went all "serious composer" on us, and you can feel that he's taken the "funny rock" format about as far as he could go.
Seriously, if you like those two, you really need to check out some of his 70's material. There are plenty of good suggestions already here in this thread, but man, it's hard to go wrong with
Roxy & Elsewhere. Still my all-time favorite Zappa.