Team Su Ho for Joo Gyung, and Seo Jun for me hahahahaa!
But for real, Su Ho liked Jo Gyung even after knowing how she looks without makeup. He has always sided with her, protected her, and cared for her. And Joo Gyung didn't like him from the start. She got to know him little by little and ended up falling for his kindness and charms. And the fact that he never judged her was just the cherry of the cake.
Seo Jun approached Joo Gyung only to annoy Su Ho. He ended up falling for her, but maybe that wouldn't have happened if he didn't approach her with evil intentions. And although his character isn't the type to get away from her just because she doesn't look super pretty without makeup (i.e. his sister), he liked her without knowing that fact. And let's be honest... in the real world something like that could change how a person feels about the other. If you truly love someone that fact won't change your feelings, but it will take a little time to get used to it since it will come as a shock (the makeup team did a good job with Moon Ga Young).
So Su Ho is the best option for Joo Gyung in the drama.