I wrote a paragraph long
Hyperion advertisement before I noticed it in your list.
Personally I think any sci-fi list that has
Ender's Game should also have
Speaker for the Dead, unless there's a strict rule against sequels or multiples, because in my opinion its the best in the series. Even if no multiples, I'd argue for it personally over EG. This is all assuming you can get over OSC being pathologically homophobic.
Also, when it comes to Philip K. Dick, your kung fu is weak. I LOVE
The Man in the High Castle, but if this list were to include multiples by a single author I would argue for
Do Androids Dream of Electric Sheep? and
VALIS as additions to the list, with Androids being a candidate for replacing Man in the High Castle for top PKD book in my opinion.
Obviously lists like these are subjectives, and I tried to qualify personal preferences where possible. OP is feel to disagree completely, of course.