statement balance = everything that is due.  If you do this you won't get late fees.

minimum balance = the minimum due reported on the previous statement.  This will avoid late fees but you will be charged interest.

custom amount = designed for people who want to pay above the minimum, but can't pay it off in full (and are thus paying interest).

BoA used to have a 4th option, but I don't recall what it was.  They have the worst autopay setup of any bank I've seen.