I use two.
Amazon KDP for the e-book.
IngramSpark Print Distributes to brick and mortar retailers, bookstores and libraries file. If you ever hope to put a print book in a bookstore or at your local library this is where you want to be. Accepted for download is only PDF. E-Book Distribution to online e-retailers but accepted download only epub. IngramSpark does NOT provide free ISBNs. Customer service is very responsive and helpful.
Createspace has very easy to use with the step-by-step instructions. You can upload your work as a print-ready .pdf, .doc, .docx, or .rtf. Your page count will be detected and an automated print check will run once your upload is complete. You’ll be able to see any issues online using the Interior Reviewer tool. Createspace does provide free ISBN or you can use your own.
Another plus is that should you choose, you can let Createspace convert and send to KDP for ebook publication.
One note: I prefer to purchase and use my own ISBN. Yes, this does add cost but also gives me a little bit more control.
So how to you convert and publish your books? Print and e-book?
Do you do conversions using third-party tools or do you let the printer tools available on their websites?