I agree with Teacher of Theatre, Hello, Dolly! for all the reasons expressed previously. Another, though not an all time personal favorite, would be Annie, purely for it's construction.
i still would have to go with Gypsy...and no not just cause i am a huge bernadette fan...cause i was w fan of gypsy before i even knew of bernadette when i was like 7...but whatever....Gypsy to me just kind of defines musical theatre!! the book is awesome, the music is incredible....there is just something about it that makes it perfect...to me that is!!!:)