There are too many variables in collision safety to say whether big is better, etc. Obviously a small car is more nimble, and a good driver might be able to get out of the way of an accident, whereas a big, lumbering vehicle (such as our Chevy 1-ton crew cab 4x4 long-bed Diesel), may not be able to in the same circumstance. If you're sitting at a light, and you see an out-of-control vehicle coming at you, a motorcycle is best. Pop the clutch and you're out of the way. If you're absolutely going to crash, then better be in a late-model full-size SUV. Plenty of metal to crush and absorb the hit, and plenty of mass to share the impact. Much less G-force on the people in the heavier mass vehicle with more crush area.
Charles