While the professional literature abounds with the values of feedback on L2 language writings, few researchers have investigated the differential effects of types of feedback on the writing improvements in terms of proficiency levels. The purpose of the study was three-fold: to examine (1) the effects of three types of feedback, teacher, peer, and self-review on sixteen Korean college students" writing improvements; (2) the relationships between feedback types and proficiency levels; and (3) students" opinions on the feedback types such as preferences and reasons. The results showed that all types of feedback helped students improve their writings through revisions, but the effects of feedback differ from feedback type to type. The effects of teacher and peer review were significantly beneficial for students" writing, while the self-review was the least effective. In addition, the more advanced writers benefit from the peer or self-review, while the less proficient writers improved their writing from the teacher feedback, even though most of the students prefer the teacher feedback to the other types of feedback, peer and self-review. The theoretical background and pedagogical implications are discussed.