If I've re-watched an anime several times without getting boring, then it must be my favorite anime indeed. In that case, my favorite would be Rurouni Kenshin: Tsuiokuhen, Vandread 1 & 2, Gensomaden Saiyuki, and s.CRY.ed.
Deardrops.
Only Riho's managed to capture my attention. So I start with her route first.
(Her behavior is somewhat a reflection of my own personality.)