Through crappy laptop speakers, A instantly sounded like "floppy picking" (as we call it in my band), at least to my ear. I could hear it immediately in the rhythm, and not so obviously in the tone (but could definitely hear it in the tone).
Listening to B only confirmed this to my ear.
That said, I expect that this could also somehow be a "gotcha" poll, and that both are picked the same way, just controlled differently...to prove the point.
There's no reason to use just one or just the other. They inherently sound different, and feel different to play, so use the one that works best. Yes, you can control both so that they sound more similar. But they inherently sound different, and it's mainly about rhythmic feel.
As for physical pain, injury, etc., downstrokes only has never been an issue for me, even at snappy tempos. It's just harder to do, not more injurious. You have to actually be good at it, and not a lot of people are. OTOH, I don't know how to slap and pull at all, while others who would fall apart playing all downstrokes are masters of it. If I tried to do it at a high level of speed and intensity, I would probably feel like I was going to injure myself too!