Although my boys aren't big dogs, I prefer medium/big. I had my heart set on a border collie(x) and was pretty mad when my mom decided on a sheltie without telling me. Needless to say, I couldn't stay mad. I prefer 30 pounds and up. For my third dog that I'm getting in the next year or so, I'm hoping for a rescued rottie, pittie or gsd. All would fall into the big dog category I suppose.