Graduating a year early?
You are obviously in a good position either way, but as you suggested, graduating early appears to be your "practical" decision.

If you are considering a doctorate or masters (it sounds as though you are), graduating will allow you to get a head start on it.

However, if you you truly don't know what what graduate degree to pick, and don't decide to go with that, consider doing an independent study with a favored professor or doing some tutoring at your local university, as it would not only contribute to your resume when applying for a masters program, but also give you opportunities to dabble in subjects you find interesting, and ultimately help you decide which field you'd like to master in.