And the third post about distributors starting with Ingram and Lulu which leaves us with CreateSpace.
I didn't use CreateSpace much, only for a single book because I didn't like it. The biggest complain with the cover. Unlike Lulu who gave exact pixel dimensions and Ingram which used PDFs but provided a template, CreateSpace uses PDFs with inch/mm dimensions. Even with my relatively decent skill with Gimp (15+ years), I never got it right. Also, CreateSpace will replace your barcode even if you got it right. The font was pixelized and it was usually not quite right for me. It was also at a time when I did bar code art (which can be used but is discouraged).
(Not mine, just use it as an example.)
The paper quality for CreateSpace books felt "thin" to me. I had two iterations of the same book with CreateSpace and Lulu and the CreateSpace one was much thinner than the Lulu. I also didn't care for the smell (a big thing for me) but a few weeks in my living room and it would smell like incense anyways.
The UI was the easiest to work with. Click a few buttons and you are good to go. Likewise, there is no change price for iterations so youc an redo the cover/interior repeatedly until you get it right. Since CS is based in the US and uses Amazon's logistics, the books showed up fast. They also have a fast-track into the Amazon system which is where the bulk of the sales will come from.
In the end, I didn't go with CreateSpace because of a number of reasons, mainly the difficulties of the cover, the barcode really bothered me, and they were an Amazon company. I have a tendency to avoid monopolies even at the expense of my own profits so... it wasn't for me. However, there are a lot of folks who use CS either exclusively or only use them to get into the Amazon network faster.