Depends on region… depends on what you want to read… depends on you e-reader.

For example a kobo or a kindle will only read from kobo and amazon respectively.

Kobo and Google Play Books is my first stop to shop, since it supports Adobe Digital Editions, along with their own apps.

Amazon is my second stop. Not because I like them, I’m I. The same boat as you. But believe it or not their encryption is based off of your devices serial number. And you can DeDRM your Kindle books very easily.

Then it’s from publishers directly if they let you, like J-Novel Club is pricy but they offer drm free books.

My last option is obscure, but cool if you are looking for a deal. Humble Bundle is where I go for textbooks and older series. Only issue is they sell only in Bundles, and you’d get a lot of stuff you may not necessarily want. But the deals are crazy if you don’t want to pirate.

Finally depending on value and how much I feel the book is worth, I may sail the high seas.