Great question! Zappa's bands have incoprporated so many great players using numerous musical boundries. I saw Zappa numerous times going back to 1971 at the Fillmore East (NYC).
I categorize Zappa in three stages. The early stage being the MOTHERS OF INVENTION (era) although FREAK OUT was the debut, the classic album from that era is: WE'RE ONLY IN IT FOR THE MONEY"; middle stage had some great players, look for "HOT RATS" or "CHUNGA'S REVENGE" "WACKA-JAWACKA", BURNT WEENIE SANDWICH", the orchatrations during this entire period are awesome; the latter stage "OVERNIGHT SENSATION" / "APOSTROPHE" although tended to commercialize ZAPPA (via George Duke vocals) these are still excellent albums and did maintain musical integrity. After 1975, the sound somewhat went through a swallow commerical sound (ala SHEIK YERBOOTY" which I do not reocmmend). Otherwise you should look for the other classics each with a different style: 200 MOTELS (soundtrack to an acid rock flick); THE YELLOW SHARK (Zappa orchatrated); FRANCESCO ZAPPA (super melow electronic harpzichord Baroque style music which is actaully appropriate for an infant). The man was a true genius. I have often wondered, if he did not die...
