To add more confusion to this topic, I'll throw in a few other options. If I had to choose what to have in a real survival situation, I'd rather have a sleeping bag. Even a cheap $10 sleeping bag is going to be warmer than either option mentioned.

Or, you could do what I did. Buy a few yards of fleece and some silnylon (regular nylon works also) and sew them together. Then you have a very windproof, nearly waterproof blanket. They sell nylon backed fleece blankets for under $20 at walmart, but they're usually pretty thin. With a little time and sewing ability you can make it for about $4, and make it any size and style you want.