I came across this interesting article on publishing with the various on-demand publishing sites. Don’t forget to bookmark the page since it lists some great sites to look into publishing.
The author makes a good point to spread out over many publishing outlets, but bear in mind that for Amazon ‘s KDP Select program, you may not be able to join other sites under their terms of service. You can publish elsewhere if you’re an Amazon author, but not if you are a member of the KDP select service.
Also bear in mind that you may need to re-format your manuscript for each service you choose. Some authors find that a daunting task since the mundane chore of formatting correcting can be frustrating for one, let alone multiple styles.
I would suggest looking into the various sites to see if they offer better pricing, distribution, or marketing features.