I thought this would be an interesting topic to explore, so here I am. Feel free to let me know if you have different thoughts on what senses our protagonists favor or if you have ideas for the other characters.

Kousuke: Taste

Kousuke is shown throughout the story to be someone who is passionate about food, especially sweets and deserts. He is a picky eater with high-end tastes. Foods that are high in sugar trigger the pleasure center in the brain, which makes sense; he eats to alleviate stress. He doesn't like to eat food that is below his standard, however, this seems to be because of social discomfort rather than taste. In episode 23, upon trying the rice cake after being pressured by Shin-Ae, he remarks that the taste is "not bad". He does dislike the burger in episode 27 however, and in regards to funnel cake in episode 87 he says "I know they're sweet but they aren't exactly pleasing to my eye. And they're deep fried to top it off..." To me, this indicates that he doesn't like greasy foods in general.

From what I can tell, Kousuke has the most rounded response to stimuli in general. He's very organized in the way he experiences the world. I'm not entirely sure what I'd put as his second most favored sense or his least utilized, so if you have any ideas feel free to let me know.

Yeong-Gi: Hearing

Yeong-Gi uses music as a source of comfort. We link this back to his mother, who is mentioned in passing to both have enjoyed music and sung Nol to sleep as a child (Ep. 129). Shin-Ae mentions that he plays his music at extremely high volumes through his headphones. She sees this as destructive and tries to discourage him from doing so, however, she hasn't convinced him yet. He plays it so loudly likely to drown out the world around him. Considering we know he doesn't think highly of himself and that he suffers verbal abuse from his family, trying to drown out his thoughts and the words of others is consistent with his character. He sings to himself in episodes 11 and 64 65.

Yeong-Gi responds least favorably to touch. This is likely due to him corelating touch with Yui, who utilizes it as a control tactic. Quim also has mentioned he's blind without his glasses and or contacts, so sight as a strongest sense doesn't seem too feasible.

Shin-Ae: Touch

Shin-Ae takes comfort in touch and textiles. It's apparent that she has abandonment issues, likely due to her mother leaving with her sister when she was still a toddler. It's possible that for her touch is a way to assure herself of someone's presence, a way to know they're with her instead of leaving her. There are two stand-out instances of Shin-Ae taking comfort from having something/someone touching her as far as I'm concerned. The first is her father's jacket, especially during the formal arc. She uses it as a source of grounding in an unfamiliar and nerve-wracking environment. It also doubles as a way to cover her revealing dress. The second, perhaps more obvious instances, are the hand holding scenes. She mentions in episode 118 that these events were "something that made me feel better".

Shin-Ae has many variations of the line "that voice" throughout the series, as well as remarking multiple times on the way things smell- Nol, Kousuke's trenchcoat, etc. Something to keep in mind, I suppose. Although she does deeply enjoy food, she doesn't get to eat much due to her financial situation. Her taste preferences aren't as likely to affect what she eats because she takes what she can get.