In my experience the production white leghorns lay the most and have the best feed to egg conversion ratio, they can handle mose climates, I am in southern Wisconsin, it gets to -18*F in the winters and 100*F+ in the summers and my leghorns do fine. Only problem is they do not live long and reproductive issues are pretty common. I have some sexlinks and they are pretty good too but they are usually pretty aggressive hens that pick on the others. They have the same cons as the leghorns. I also keep Production reds, they have been the healthiest out of the three but don't lay as much. I also keep lots of dual purpose breeds, they are decent layers and they live long. Egyptian fayoumis do well in the heat, so do Golden Campines, but they do not lay as much as the others and they do poor in the cold. I can't really just suggest one based off of what info you gave. Do you want to keep and breed a certain breed of chickens or are they just going to be bought for eggs and then culled once they slow down? What's going on besides high production?