Hmmm... that's a good question... Pearl definitely obsessed over Rose a great deal more that Greg did, but that comes down more to the nature of their characters. Pearl, for the longest time, pretty much defined her whole existence around her connection to Pink/Rose, which of course is understandable given that she was literally made to serve her. Like AlyssaStehle said, Rose wanted to be on equal grounds, not just with Pearl and Greg, but with everyone inhabiting Earth, so Pearl's inability to see herself as anything but subservient to Rose most likely was frustrating for her. Therefore, despite genuinely caring for Pearl with whatever variation of love she had for her, this would inevitably put a strain on things, and would in and of itself make her more drawn to someone like Greg, who admired her for everything she was, but also had enough self-respect to not follow that unhealthy path.

Of course, that analysis became more about Rose's feelings for Pearl and for Greg than about their feelings for her... but on that point, I honestly don't know how the "quantity" of love for someone from one individual can be compared to the love for that person from another individual... It is a concept that inspires one to think, however, which is always good.