Some of Heinlein's early works and Time Enough for Love - although I hated "Stranger in a Strange Land." A lot of Asimov.
Simon Hawke's "The Wizard of 4th Street" series, including "The Nine Lives of Catseye Gomez."
John Morrissey's Kedrigern series.
McCaffrey of course.
I can't pin down a favorite.
However the reason I love them is that they got me through puberty, when it was hard to relate to the people around me. I'm still trying to stamp out some of Heinlein's political stance that got absorbed in High School.