Bradbury & Vonnegut if you are gonna stay in the same time period. Delaney, PKD and Gene Wolfe are my favorites of all time, they are 10-20 years later but I think they raise social and philosophical issues that resonate to this day.

I liked the foundation books its just always been a pet peeve that Foundation, Enders Game, and Hitchhikers Guide are always listed as greatest of all time. They are super enjoyable books but not like... what I would choose to represent the genre.