Here is my 2 cents -
I think I will be getting Buckeyes for my dual purpose birds. Research says: Rose combs to avoid frostbite in winter, decent size, love the color (close match to my Irish Setter?), good at free-ranging, some broodiness, lay a medium-to-large cream colored egg. Check them out in the Breeds page here on BYC, very pretty birds. Hopefully, I can find some quality chicks when I am ready.
I would like to keep a dual-purpose flock, butchering chickens both as needed and as a mass cull in fall. Maybe learning to caponize if possible to extend the butchering age of the roosters so I don't have to fill the freezer with chicken, I would like to save some space for venison. :)
With the Cornish Cross chickens, you usually have to order them from a hatchery and there is usually a minimum number to order. Many stores only carry chicks in the spring, so you would need to buy however many you want for the year, all at once. Since they have such a limited lifespan, you don't have much choise of when to butcher them - in some cases a week or two can mean the difference between chicken in the freezer or dead birds out in the pen. If you have a source to buy just a couple of the cornish cross at a time, you could probably keep a flock of different ages - say get 4 chicks every other week. Then you would be able to keep Cornish Cross (Broilers) and just butcher a couple at a time and keep your family in fresh meat.