They would all be good fathers, they are all sweet and lovely with kids, but I think Harry would be the best. He has a great relation with Baby Lux, he takes good care of her, he is patient and 你 can see that in my icon.
I think both Liam and Louis would make great dads. Liam, of course, since he's very mature and responsible. Louis would make a great dad because he has a lot of experience with kids, having 5 sisters. Again, both Liam and Louis would make great dads. :-)