How to pick a flock rooster?
For me it was easy. There is a joke at my house, pretty much all the chickens answer to "chicken"...and if they make any aggressive action towards a human their name gets changed to "Chicken Dinner". For picking between the nice ones I usually think about which I would want all the chicks to look like, I consider size, presence, feathering etc. I also look at my hens and decide which rooster would compliment them the best. Maybe if they are BIG hens, I could use a smaller rooster that had better color / plumage etc. If they were smaller hens and I wanted to improve size with the next generation I'd use the biggest roo.
2 Australian Shepherds, 8 horses, and currently suffering from the effects of chicken math with >30 chickens and climbing. Especially fond of Silver Penciled Rocks and Cochins but have some polish in the grow up pen along with some Easter Eggers.
for a backyard Roo, disposition is important. Other than that, look and make sure there are no physical deformities, pick them each up and feel the breast area, the thigh area. All of the roo's I am assuming have had equal opportunity for the same feed and exercise, so you want the roo that has the most thickness on that amount of feed.
If you are serious about improving a flock, you also need to keep records, and it would be best to pick a roo that was well developed and came from a good laying hen.
With 'pan fry' roos, you need to be particularily careful about aggression towards the hens. Meat roos are notorious for being violent and hard on hens, and need to be monitored and culled for even the slightest hint of that behavior.
After that, the usual standard list applies:
Does the roo watch the skies and alert the girls to danger?
Does he call them over for food when he finds it, instead of eating it himself?
Does he protect and escort chicks?
Does he break up fights?
Is he gentle when mounting? (no feather-pulling/spurring/etc)
and perhaps most importantly: Is he human aggressive?
Please note that nowhere on your list should you have a requirement of 'is my rooster cuddly/ amenable to petting." That would be a nice bonus, but your rooster has many more important jobs to be responsible for than entertaining humans. His hens and chicks should be his top priority.