If you have never read Robert E. Howard's Conan stories, or not in their original (unedited) versions, these are the three books you should read:
The Coming of Conan (book 1)
The Bloody Crown of Conan (book 2)
The Conquering Sword of Conan (book 3).
These are all published by Del Rey books. They include "The Hyborian Age"; Hyborian Genesis; Notes on the Transcripts and Chronology; and the Notes on the Original Howard texts.
The reason these books should be considered above all others, is the original text, which were not published between the 1950's and the release of this series of books in 2003.
What is the difference?
Robert E. Howard was a writer and product of the 1920's "South". His writing reflected both racial and misogynistic leanings that were edited out for most of the published works that many of us grew up reading. For me that was the Tor Publishing books which brought Howard's and De Camp's stories together into a series of 12 novels.
Having read both versions, I found the originals to have lost some of their grittiness in the editing process. I also didn't find the parts that were edited out to be all that offensive anyway, but I'm a purist when it comes to freedom of speech.
I as a trained / educated historian also don't believe in what I call "chronocentrism", which is when we take social mores, ethics or sensibilities and retroactively apply them to previous generations. What we may consider to be morally wrong today, was likely not believed, or even understood as being morally wrong multi generations ago.
That being said, the books can be purchased via whatever online seller you choose. If you use Amazon, they can all be purchased for less than $45.00 and in their soft cover format (which I recommend because they are better and actually cheaper than the Kindle version).