I have not found the way a roo to be raised to have much of a factor as to how aggressive he is. It has more to do with the personality of the bird. Nature vs nurture, and nurture only goes so far before nature takes over. Sometimes, the roo is a real sweetie, or at least non aggressive, until his hormones kick in. Then, they either get to tolerate their owners or they don't. Also, I'd rather take the boss roo in a flock over a subordinate, because you cannot see the true personality of the roo that is at the bottom of the heap. When our boss roo died because of a freak accident, the second roo took over. Soon, the sweet rooster I had raised from a chick put his three-inch spurs into my knee, and we could not go into the coop without a grain shovel to protect our legs or wedge him into a corner so we could feed and collect eggs. Maybe this was just a one-time occurance, but you might be able to say it made it's mark on me.
I have found that production bloodlines have some really nasty roos. Most people say Buff Orps, Barred Rocks, Australorps, Brahmas, and Cochins are very docile, even rom hatchery stock. But a nice, quiet mutt off craigslist will also do the job. I'd just pick a nice docile boy and go for it, the coop is empty without a rooster. You might also be able to get an exhibition breeder's culls, birds that are not good enough to be shown but are more than able to become flock roos. This would be my first choice, because then you get a big, pretty bird who is used to people and is most likely not aggressive.
I have found that production bloodlines have some really nasty roos. Most people say Buff Orps, Barred Rocks, Australorps, Brahmas, and Cochins are very docile, even rom hatchery stock. But a nice, quiet mutt off craigslist will also do the job. I'd just pick a nice docile boy and go for it, the coop is empty without a rooster. You might also be able to get an exhibition breeder's culls, birds that are not good enough to be shown but are more than able to become flock roos. This would be my first choice, because then you get a big, pretty bird who is used to people and is most likely not aggressive.