You really are not going by breed. What works for me, is to thin a group like this in stages. There is always the fear that you cull the wrong one, and it does happen, dang it.
Fist cull, be rather heartless - but anything you don't like, off with his head. Divide the boys in half, half stays, half goes - so that leaves you 4.
Wait 4-5 weeks. Again, anything you don't like now, for what every reason, cull, and cull anything that is the least bit aggressive, crows a lot, fluffs up at you. But take a good look at them. Check their feet and beaks for alignment, weigh them, (they all have had access to the same food, who does better on least?) Feel their breast bones.
Again divide in half - keeping two. Wait a couple of weeks. At this time either they will be both acceptable, or there will be a winner. Cull the last one.
Mrs K