I recommend that folks just purchase a bunch of books by both men and decide for yourselves....I own most of their books collectively and enjoyed all of them. I enjoy also the fact that people refer to Jack in reference to the .270 like this is all he was known for and although it is true that he helped to make it wildly popular (still today), he admitted that the 30-06 was an all around more versatile and useful cartridge and that he also esteemed the 7 mm Rem mag in high regard as did he the same for the .375 H&H and .416 as well as the .338 and used them all effectively on African dangerous game and plains game...both he and his wife were fantastic shots on game and shot running jack rabbits for practice in the off seasons....he loved a rifle and shotgun and was a fan of the handgun and owned several but wasn't so much an enthusiast of them as he was for the long guns....
I loved reading Elmer Keith's stories about shooting caribou at a distance with the 1st two S&W 4" model 57 .41 mags which were gifted him...his stories of long shots with the .45 Colt in his early days, his use of the .280 and .285 Dubiel/OKH, his reviews on leather and Buck knives, Ruana Knives, boots and hunting/outdoors' clothes and gear....
I would 1st recommend by Elmer, "Sixguns" and "Hell I was there"...
And Jack, "The Hunting Rifle" and "The Rifle Book" and "Jack O'Conner"
All worthy and entertaining and they have great value to me as I grew up in central Montana as a 4th gen kid born and raised there...cheers...