I think this comparison is not suitable or relatable, Bitcoin and USD are both in a different aspect, both have a different aspect. For me, Bitcoin is the best but if maybe happened that another person would choose USD because of the acceptance. So the comparison should be based on reality, Bitcoin isn't getting accepted the whole around the world but USD did it for many years, that's the main point.
But if you pick out for the future purpose then Bitcoin should be chosen easily by any people who have a little idea about the Blockchain system. So the choice is different.
You are right, it is not appropriate to compare the two, btc and usd. Each is in a different area, legal and not, obviously USD is accepted throughout the world, while BTC is only in certain countries. But on the other hand, Btc has great potential and is very worthy of being an investment, as long as we must accept all risks because the price is very volatile.