North Roads rule. Or, something like the On-One Mary bars, which is a derivative. For the most natural position, they are about as close to human perfection as you can get - unless you demand a higher performance design. MTB flat bars are designed for maximum wide grip control in tight situations found on trails - period. As such, they do not lend themselves to long ride comfort. It is rare that a rider can get comfortable with them over any road ride beyond 35 miles. People can spend whatever, trying to keep using those flats, but the wrist pronation will eventually introduce carpal problems and sore elbows at the ulnar socket. Only apes can maintain that kind of twist and get away with it for long.

North Road bars and their variants allow the entire arm to rest in a natural position without that bend in the wrist - the one that forces the heel onto the bar of flats. When properly setup, there is a crook in the elbow and the carpal bones are alined with the forearm. Billions have been made over the decades, with drops being the defacto bars for racers and those who get hooked by the marketers. I'm not saying drops don't do a good job getting riders out of the wind, but I don't think many people really depend on that low position that much.

If I were looking for a non-drop option, it is ther NR I go for every time.