Better to be too cold. First of all, it's alot easier to fight against, just put more on. There is only so much you can take off. But, ultimately, it's just less unpleasant. When I'm too hot I feel my brain slowing down to a crawl, and every part of my body is in disconfort. When it's too cold, parts of me feel warmer, and those that don't, hands, ears, are easy to cover.