One Sweet Day spent 16 consecutive weeks at #1 on the Hot 100 and was crowned the Hot 100 Song Of The 1990's.
We Belong Together spent 14 weeks at #1 on the Hot 100 & was crowned the Hot 100 Song Of the 2000's and is her biggest airplay hit with 16 weeks at #1 on the airplay chart.
All I Want For Christmas Is You is her biggest selling single in the US with more than 3 million copies sold and always dominates the Holiday season every year usually becoming the most popular holiday song in airplay, sales, & streams.

Which song do you consider her biggest US hit?

WBT>>>> it's soo timeless and my fav song ever!!

A few years ago To think that AIWFC would be considered Mariah's biggest hits would be absurd but yaass get that classic crown

I still think it's WBT