Many authors who want to self-publish think they must choose between Amazon KDP or Ingramspark; you can choose both for different exposure. #selfpublishing
Additional thoughts from https://sleepingcatbooks.com below on how to approach Ebooks and Print books.
Ebook: If you don't use KDP Select, go direct where you can (KDP, B&N, Kobo, Apple Books, Google Play) and use Draft2Digital to reach the rest. Do not use IngramSpark for an ebook. By going direct where you can, you'll have higher revenues, more control, and access to any promotional opportunities the individual platforms may offer.
Print: KDP and IngramSpark together, using the same ISBN (that you own) for the same edition through both. Set up the project on both platforms through entering the ISBN, then save that project as a draft on both platforms. Do not enable KDP Expanded Distribution. Do not set a future launch date on KDP. Once that ISBN is in both systems, you can proceed with publishing in whichever order you like without either claiming the ISBN is already in use.