First, I would identify needs of the person using the edition and how the edition will be used. Is it a student new to music, a university student, an educated pro, a music researcher? Go from there. For example, a puritan urtext edition may not be the best choice for a students first book on Bach. Likewise, a verbosely commented edition with overflowing editorial opinion, may not be the best choice if you were doing music research and publishing references to it in a journal.
Do a bit of research, see what editions are being talked about. Editions go in and out of fashion.
Grab at least two editions and compare. Look how the editors approach the presentation of material.
Hold an edition in your hand. Ask yourself, does this work for my purposes?