Jane Espensen confirmed that Rumple wasn’t Regina’s father. As for Rumple being the safer person to be the dark one, the saying “Better the devil you know” springs to mind. Rumple at least had a heart, literally, whereas Cora was all about the power.
Did anyone think Rumple was a little bit taken aback when Cora told him she had ripped out her own heart in FTL? Almost like he thought such an action was wrong, even by his standards?