[Fallout]

I think that's too general mate. A big blubbery fellow will have a lot of elasticity to decelerate his mass more slowly which is good, but also have more inertia. I'd rather be chunky in a stop dead impact, but if I was going to hit something with a glancing blow the skinny bloke will change direction much more easily.

In summary:
Right into the side of a car = best to be fat
Glance it with your knee or shoulder or hip = best to be skinny!