I'm not an expert on this by any means, but I think it really depends on what you're wanting. If you want a rooster primarily to protect your hens, especially if they're free-range, look for a dominant rooster, he may be slightly aggressive, but he will make sure his girls are safe. If a rooster cowers from you, he may not be a good protector for your girls. If you want a friendly rooster, I'd pick out the one that seems to be the least dominant. Aggressiveness also depends a lot on breed. If you know what breeds you have, look them up and see which ones tend to be less aggressive. If you have kids you do not want an aggressive rooster! Hope this helps!