I chose the .500 because of the modern case size. The .45-70 case is just too big for smokeless powders, especially if the rounds are downloaded. I download a lot for fun shooting. Some love recoil, I tolerate it when I need to. I like having the potential, but don't need to use it every day.
The secondary reason I picked it, is that .50 caliber is just neat.
JMHO
mike