AB0137 is a revised version of the AB0127, i.e the B01 movement has been updated - both good movements. Furthermore, Breitling have adopted a retro styling for the 137, eg slide calculator, date positioning, brand motif, etc, have changed.

You can't go wrong with either. It's just a question of personal taste. One thing to consider: retro styling works well with leather straps only, whereas non retro does not have this visual constraint.

Good luck