Heinlein's works, especially the stuff that started out as pulp/magazine fiction, is such a huge part of my young life. I've worn out multiple copies
of Stranger in a Strange Land and a copy of Time Enough for Love.

I've read all of the other authors mentioned and like quite a few of them, but no one ranks higher than RAH.

Niven and Pournelle. Greg Bear is good too. Also, Kevin Anderson. Poul Anderson is not bad either.
Ben Bova has a cool series about the Solar System. Just started reading Pratchett's books.

-SH