Is it better to buy a book or buy an e reader that has books?

I love reading. But lately I've been so busy I can't even go to the library and get books anymore. Is the "nook" or " kindle" worth it? Is there another device that does what those devices do.
But I just want to know if I do buy one of those do I have to purchase the actual books in it? Because that will be very expensive.

But then again. I'm gonna miss having the actual book with me. You know it's actually better to have the actual book instead of reading it on a tablet of some kind. But books can get too bulky and soon I'll have my own library. LOL!

-if I get the nook/kindle do I have to purchase books or do I get an unlimited choice?
-is it better to own the book or read it on a device? (Just out of curiousity)

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