If I had the opportunity to add either to my personal collection, I would chose the Johnson due to its rarity. In a combat situation, I would grab the carbine. Not a lot of stopping power, but from what I understand it was more dependable than the Johnson.
Me too,primary choice remains for Johnson,not only for its rarity ,in remembrance of its wide and extensive service too.I remember that my father was fascinated with the machine in a way that whenever he got a chance to tell about LMGs,first he started with Johnson.We were too soft in those days to catch his words,no joke,please. The only thing I dislike of its left side box feeding system. Stopping power was good enough, .30 Carbine M1 was the most produced small arms in American History.