Mariah's had the biggest in numbers but with the most ups and downs from 90 - 08
Beyoncé has had the most consistent career seeing near constant success from 1999 - present
Janet had the most memorable moments and influence of the big 90s girls (with Bey being representative of similar iconography in the 00s and 10s) but saw the most abrupt failure (though thats kind of hard to pin directly on her)
Not really fair to compare. Janet and Mariah are both at 25 years + in the industry, while Beyoncé (even with DC, which all of ATRL likes to pretend wasn't part of her career) has only had 18.
I was just listening to "All I Want For Christmas Is You" yesterday too!