What makes the perfect science fiction novel? Well, there’s a post at Ask MetaFilter that thinks the perfect book is one that achieves the holy trinity of “rollicking story, fascinating technical detail, and characters [you] want to cry over”. The poster also asks for examples. It’s all subjective, of course, but several examples are given. The thing with “favorites” is that it all depends on a person’s tastes and experiences. What’s enjoyable to me might not be enjoyable for everyone.
This link comes from Folded Space who seems to think the question was not answered and has some thoughts of his own. Good reading all-around!