I feel like an "IT girl" has the most attention, like brand endorsements, articles written about them. They're typically considered fashion icons. Some of that attention could be negative tabloid stuff though.
This often correlates with the "most popular" celebrity, but not always. Popularity could be measured in other ways like chart success, talent, career longevity, and likability.
For example I would consider IU to be in the "most popular" category, but not an "IT girl". Jennie is an "IT girl" with all her endorsements and social media followers, but her career doesn't have that much going on and she isn't universally liked with all her scandals.
