Almost exclusively on my iPad mini. I "carry around" multiple technical references, newspapers, academic papers, the current novel I'm reading plus the next few I have lined up.
I commute most days and travel a fair amount so having access to most of the written material I'm likely to need day to day is, if not critical, at least very, very handy.
The novels I mostly get via Amazon. The rest from multiple sources.
I like to read from paperback/hardcover. Never enjoyed reading from kindle/ebooks.
Technical books: via paperback/hardback
Any other book: Audible
From the library if possible otherwise used when practical.