To keep this seven year old thread alive, I figured I would register on these boards.
I have been a Heinlein fan for a while now and have recently purchased someone's collection so I am looking forward to making my way through 35+ Heinlein books, but I wanted to share my favorites.
For anybody who hasn't read it yet, Have Spacesuit, Will Travel is by far my favorite Heinlein novel. It is just such a well rounded novel full of wonderful plot twists. While the concepts he came up with in Stranger in a Strange Land are some of the most amazing out of all literature in my opinion, some of his ideas in Have Spacesuit were what really got me to love Heinlein's work. From the Mother Thing and her people, to the galactic court at the end and the fact that it was located in the Lesser Magellanic Cloud, this is by far a must read for any Heinlein fan.
A close second would be Citizen of the Galaxy. What I especially enjoyed in this novel was the idea of The Family and how Heinlein created such a unique universe for this story. I really feel like the Nine Worlds/Hegemony/Family parallel could have made way for an entire series of novels that were just as compelling as any other. The fact that all of this is just in the background of the novel really show how much of a genius Heinlein will always be.
That being said, when I think of Heinlein's work I see it as being written by two different authors. His early stuff varies so much from his later work, yet both groups are masterpieces in their own right. I will always have a love for his early work because it has that romantacized SF feel to it.