To me that is a hard choice, especially if your only criteria is behaviors. At some point they will determine which one is dominant. That may be by serious fighting or you may not even notice the process. What I typically see is a few skirmishes where one decides that they are better off running away than fighting. Part of that is that they have to have enough room to run away and get away. If they don't have room to get away the winner doesn't know he won and keeps attacking. Or if the loser hunkers down and tries to protect his head the winner seems to think I have him beat, I better finish him off now. Lots of room does not mean they will reach an accommodation but the more room they have the better your chances.
Once they determine which one is dominant the dominant one suppresses the behaviors of the submissive one if they are kept together. The dominant one has certain duties and privileges in taking care of his flock. If the other one tries to do too much the flock master may not be happy. There is nothing consistent with this. Each chicken has its own personality and each flock has its own dynamics. You might see different results one year to the next as you keep different birds. Sometimes they may work out a power-sharing agreement.
Sometimes the presence of a rival stirs up the dominate one to behave in ways you don't want with the girls, even if they are not fighting. If you remove the rival he may calm down some, may not though. If you remove the dominant one the behaviors of the one that is left will change since he is no longer suppressed. Could be for the better, could be worse. And behaviors can change as they mature. I consider the maturity of the pullets have a part in flock behavior too. They have a part to play in flock dynamics.
This is the type of things why I say it's not always an easy choice. Personally I like an early maturing cockerel, not just because that helps with my raising them for meat goals. In my opinion (all this is opinion) early maturing ones tend to have stronger personalities so they can eventually win over the flock by personality rather than having to rely on brute strength when they mature enough to do so. They can be pretty rough on the pullets going through puberty though.
My suggestion is to observe and do the best you can. To me human aggression is a disqualification. During puberty they will probably be pretty rough on the pullets. To me that's just them being chickens and growing up in the flock. That can be really hard for some people to watch and a lot of cockerels literally lose their heads because of that behavior. Typically they grow out of that behavior, but not always. But if one seriously injures a pullet, well that's another disqualification to me.
Good luck. Odds are you'll be OK with whichever one you choose, most turn out OK once they get past puberty.
