I've had both Buff Orpingtons (still have BOs) and Barred Rocks and they are both very cold hardy birds. The lay rate of the two breeds is about the same (3, occasionally 4 eggs per hen per week). Barred Rocks are normally docile, although on very rare occasions, I've had an aggressive one. I've never had an aggressive Buff Orpington in my flock, and they are a wonderful breed for children; friendly, calm, and gentle (my children, and now my granddaughter, made lap pets of ours).I'm kind of leaning towards 2 buff orpingtons and 1 barred rock. Just because I understand they are hardy enough for the minnesota winters and friendly enough for my kids.
fellow Minnesnowtan. LOL. Buff Orps and Barred Rocks are great breeds. I have White Rocks, ( Which are the Barred Rocks cousin ) and Rhode Island Reds. Both are great breeds as well. 
