The Comets and ISAs are excellent layers and have nice personalities, but I would only recommend them if you plan to cull them around their second year. Because they are bred to lay daily, it really takes a toll on their reproductive system and the rest of their body. In my experience, my Comets SERIOUSLY suffered from some sort of reproductive issues eventually and I culled them just because I didn't feel it was humane to let them suffer. I did not know any of this before getting the Comets. They really are great personality-wise, but it's only humane to cull them. Chickens are tough and don't show pain until something really bothers them. So they likely suffer from reproductive issues and pain way before we can realize it.
I've never had Leghorns, but I've heard their personalities aren't the best. Great layers though. I LOVE my Barred Rock. She's hilarious! She's quite bossy and also "complains" to me a lot by making this "bwaaaaaaa" noise like she's warning me she's gonna do something bad if I don't give her a snack ASAP lol. She also likes to peer in at me from the back step when I'm inside, hopeful for a treat. I think Barred Rocks are generally spunky like this, from what I've heard. They aren't known for being super sweet and cuddley (but they can be), but they are a great flock addition because they are friendly, have big personalities, and are solid layers. Mine is not aggressive at all. She can sometimes boss the other chickens around a bit and puts the pullets in their place, but she's never excessively rough. Just a good chicken all around. I think she is over 3 years old (idk age because I adopted her from a rescue farm) and she still gives me 4-5 eggs a week.
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The one and only, Big Rhonda.