I always regret that my SF books are less popular than my Fantasy. SF actually takes more work to write! Personally, I believe that my output is equally readable in either genre.
I am fortunate that every one of my published books is still available, but I fear that this situation is likely to change in the near future. E-books do have a slight maintenance cost, and contracts allow publishers to discontinue them when profits turn negative.
Two books that I especially love and that I believe may be at risk are Pock’s World and Wildcatter. Both are SF, but if you are a fan of my writing, please do try these. I promise that you will meet some lovable characters (in hateful situations, of course).