They are entirely too young to evaluate beyond major DQs like deformities. IF I HAD to cull one of these now, it would be this one. That comb is likely going to be HUGE (not good) and you said he is the smallest. Beyond that, there is no determining the important points at his age. I vote you keep all three until they are about seven months old and then decide which one to use, which to keep for a reserve, and which to cull.
I somehow thought you would say that. LOL.
This afternoon I went out to the hoop to bring them in for the night. It is still too cool to leave them outside in the coop (it got down to 56 in the coop with the heater on last night), and had the cat carrier I use to transport them sitting in the corner of their run. One of the little cockerels (one of the first 2, not sure which) went over to the door of the carrier, chirped authoritatively and went in. 8 of the little pullets and 1 cockerel followed him in. They just waited patiently for me to catch the others and put them in. He is clearly a leader. I need to figure out which chick it is, though.
Nice little birds. I'm enjoying watching the develop their own personalities.