So, I know this is an old thread, but maybe someone will see this. Personally, we've had a Buff Orpington rooster, Black Ameraucana roosters, a Dark Brahma rooster & an Ayman Cemani rooster. As far as a flock watcher, I'd say the Ayman Cemani hands down. Ours is 9 months old, we've only had him for 3 months & he was a solo bird from for 4 months (without hens, previous owner), but let me tell you what. This guy flies up & roosts ontop of the door frame (7ft up) every night to watch over the 14 week old flock in the next run & make sure they all get into their coop safe. He is the most alert rooster we've had to predators, if he makes a certain sound EVERY chicken we have in all 5 runs immediately disappear under their coops!! I have heard similar stories from other Cemani owners as well. The only downside is his bites are pathetic. I'm not trying to raise an aggressive bird, I'm just saying he's not the one I'd want to see go up against a predator, poor thing...
From experience my second pick would be Ameraucanas...true Ameraucanas, not EEs. We've had a few and they are very predator aware also. My Black Ameraucana rooster who had a broken upper beak at the time (poor thing has crossbeak, very susceptible to injuries) saved our Orpington hen from a Coopers Hawk early one morning. The hawk had her too, poor thing had claw marks from her chest to her tail where it had cut her feathers. Neither one of these roosters has ever shown any aggression towards humans either, in fact my 6 year old carries the BA around whenever she wants...and he let's her.