My preference is to display radio buttons vertically per common recommendations, per some research on completion speed, and to take advantage of Fitt's Law.
However, I often get push back with regard to space constraints. While I'm moving ahead with my recommendations, I would like to hear from Devil's Advocates for alternative approaches. Here are a few I came up with, available here: https://docs.google.com/file/d/0B_vkC3_ZQ0bkT3ZKcTNBLWhNNVE/edit
Any suggested alternatives that you think work better than what I have?