가 제일 좋아하는

… likes best

→ 가
phrase Uncommon #9,090
… likes best 가 marks the person doing the liking. This phrase usually comes before the thing they like best.
KO: 민지가 제일 좋아하는 음식은 김치찌개예요.
EN: The food Minji likes best is kimchi stew.

아버지가 제일 좋아하는 노래 였어요

It was my father's favorite song.

— 블라인드 멜로디 (2018)