So the big one is Amazon's Kindle Direct Publishing. They have the best rates, and the print quality is pretty solid.
For selling on Amazon, they're the way to go.
The problem is that even though Amazon offers expanded distribution to other stores, other booksellers may not want to ever stock from a printer owned by Amazon. Which is why I also sell my books through IngramSpark. IngramSpark doesn't have as good rates as Amazon when you sell there, but their rates are about the same when you sell through other book stores.
So I do both. I put it on Amazon and then choose not to use Amazon's expanded distribution. Then, after the listing was live on Amazon, I set up the book on IngramSpark (you'll want to do things in that order so Amazon doesn't pick up the IngramSpark listing first)