My bantam buff brahma does just fine with standard lavender orphington's.In my experiences I like the bantam cochins. They are big enough to get the job done and make great flock roosters. Smaller breeds I would avoid if you want fertile eggs. Those sometimes just mate the hens back. My bantam EE also seem to get the job done. If you hens are very large you may have problems. The plus side of bantam roosters is I don't get bare backed hens anymore.