If I had to pick a favorite Zappa period, it would have to be that mid-early 70's period (Wazoo, Roxy, One Size, but don't forget Over-Nite Sensation) because of the jazz-fusion angle. That's some wicked fun stuff. I've been a Zappa fan since that period, and it's the one I tend to return to the most.
George, make them dance.
Dit!
I agree that there's a lot of jamming and improv on Hots Rats. When I said it showed sophistication, it was in the context of a first serious instrumental opus (whatever that means). I wouldn't say it's "better" than his later stuff, I just enjoy it more. There's something about the raw, young, indulgence of it all, the whole package, that I find really exciting. Any time I go back and listen to the first or second album by a band or artist that's been around for decades, it's a neat trip. There were The Mothers, but this was Frank's first solo album.