All things being equal the neck pup is "louder" because the string vibrations are bigger there, so the pup produces more signal, so usually you want the hotter pickup at the bridge to compensate.
But all things are not usually equal. Two identical pickups will sound different in the two different locations. So balance may really be how much of each pick up you want to hear. Both those bases have separate volumes I think, so if one is a little too much you should be able to roll it off a little bit and that will balance too.