がちApt to do, Tend to do, Prone to do

Both express tendencies or patterns of behavior, but they differ in tone and usage. がち attaches to verb stems, and is neutral, used for tendencies that happen often, e.g. つい忘れがちだ ('I tend to forget.'). きらいがある follows the plain form of verbs and is typically used only for undesirable tendencies. Unlike がち, it can also express a tendency to not do something, e.g. 人の話を聞かないきらいがある ('He tends to not listen to others.').

Both がち and っぽい describe tendencies or characteristic qualities, but differ in nuance. がち is neutral and used for tendencies that happen often, e.g. つい忘れがちだ ('I tend to forget.'). っぽい expresses an inherent quality or the appearance of something, similar to the English '~ish', e.g. 子供っぽい性格 ('a childish personality').