Gallinamama, Your neighbor may think round is best because tree branches are round and that works out okay for native birds. Chickens are native. They are originally jungle birds and they're feet have evolved for walking. They roost at night to avoid predators. Here they need to be able to roost on something that is wide enough that they don't have to hold on. They then lower their bodies onto their legs and feet and expand their feathers creating air spaces that improves the insulating quality. A chicken on a round perch must hold on and if you observe them they are constantly raising up and down trying to maintain position. Their feet are exposed and their feathers are held tight to the body.
Remember just because someone has always done something doesn't mean they are right.