"치마" is the best appropriate. "자락" means lower part of a skirt, it is not used commonly except a few idioms. "스커트" is direct reading of the English word skirt, that has more modern nuances than "치마".

English word "skirt" means 1. the part of a gown, dress, slip, or coat that extends downward from the waist. 2. a one-piece garment extending downward from the waist and not joined between the legs, worn especially by women and girls. 자락 or 옷자락 means #1 of the meaning. 치마 and 스커트 both mean #2 of the meaning. 스커트 is same to 치마 but usually used for Western style skirt.