I like too look for, above all, a roo who treats his hens well, and who won't attack humans. How old are yours? If you could maybe pick your top three or so, and then keep them until they're six or seven months old, you'll have a good idea of their temperaments...
#1 - NEVER attacks a human.
#2 - Calls hens to food.
Also I like to see him court the hen first (spreads wings and prances in a scooping motion in front of her). I read an article somewhere that said that in olden days a rooster would court a hen, and only breed her if she accepted, and crouched to allow him to breed her. Which was much more gentle for her than being chased, finally caught, and roughly held by the rooster while being bred. These days many roosters don't court the hens, and instead they just run them down.
I have three roosters, one of which has a date in a couple weeks with the big black pot... He's good for #1, only occasionally does #2, and never courts a hen prior to breeding her.