For something humorous and a bit off the beaten path, I'd recommend the Retief series by Keith Laumer. [1]
For the best SciFi in general, I'd actually suggest you check out assorted collections of short story. I don't have a specific anthology to recommend but I have yet to find a published collection at my library that was less than thought-provoking.
For the classics, you can't go wrong with Hugo Award winners. [2] Your local library probably has most of them; try starting with the old ones and working your way through.
For the best SciFi in general, I'd actually suggest you check out assorted collections of short story. I don't have a specific anthology to recommend but I have yet to find a published collection at my library that was less than thought-provoking.
For the classics, you can't go wrong with Hugo Award winners. [2] Your local library probably has most of them; try starting with the old ones and working your way through.
1. https://en.wikipedia.org/wiki/Jame_Retief 2. http://www.thehugoawards.org/hugo-history/