Letter size or legal size, which should I buy?

Letter (8.5" x 11") is the right answer for the vast majority of home and small-office users, since most documents you print or receive are letter size. Legal (8.5" x 14") is mainly relevant if you regularly handle legal contracts, deeds, or older medical files. Reviewers across organizing subreddits warn that mixing sizes in one drawer causes the smaller hanging folders to sag, so pick one standard and stick with it.