I use two Createspace (Amazon) and recently Wargames Vault. With the recent release of my WW2 rules, I was surprised to see that Wargames Vault is by far the best sales avenue. A little more tricky to get the books up there and the royalties are less but if the rules are selling better through that, then thats the way to go.
Professor Badger's Quasi-whimsical Pseudo-Tactical Simulation of Military Encounters of a Science Fiction Persuasion at the Company Level. an expansion set of rules will be releasing by the end of this year, and a print edition to follow