Obviously, my preference would be to finish off in a woman's mouth and I'm fortunate that I have a wife who not only likes sucking cock but also enjoys swallowing every last drop when I come.
Only once or twice did I come in her mouth and most of it drool out instead of her swallowing and that was a result of her not having my cock all the way in her mouth when I came.
I've rarely come on her face during a BJ and most of the time it was accidental when again, the timing was off and I came before she could put it back in her mouth. The only time I choose to do it on purpose, most of it shot past her face anyway and landed in her hair and the bed.
But like the answer above, one of the choices should be what one's partner wants and is comfortable with.
My preference is just that, a preference. Back when we used to swing, I also made sure to discuss with the woman ahead of a BJ, what she preferred in case I came, though only one was able to get me off and she was comfortable with me coming in her mouth.