I wasn't aware that there was a single protest event that included 10s of millions of people in the US. If you count all people that were involved in any protest during the last year, I'd expect the numbers in HK to be significantly higher still.
It's also not a competition, nobody is trying to diminish the US protests, but I don't think that events of a similar magnitude would have gone down as peaceful in the US.
Both are extraordinary, it's not obvious to me who should win the "most well-behaved protest movement" award