i'd highly recommend apostrophe as the next studio album. i think of it as the flip side to "Overnite Sensation." "Tinseltown Rebellion" would also be a worthwhile port of call. It has a little of everything, comedy tunes, doo-wop, screaming guitar and intricate instrumentals. I have about 50 Zappa titles. I think that "Ship" and "Civilization" are a bit much for the Zappa novice.
"Live In New York" is also a worthy consideration.