I think the best way auto safety is summed up is:
Size is an advantage in all kinds of crashes.
Mass is an advantage in only 2-vehicle crashes.
Rather than changing the cars, it would be nice to have everyone wearing 5-point seat belts. No, just wearing their seat belts correctly would be nice.
I personally don't think the 2010 MINI cooper performed well in the crash test. Its front end is too short; the crash dummy in the test recorded 48g of deceleration.
The side impact test: 69g
My 1993 escort (16 years older!!) had 42g of chest deceleration in the same test.
(no side impact stuff was around then, so I suppose my car might be the same or worse there... plus I don't have side airbags)
Adding length is great for economy and safety. My Kammback helps rear-ending, and my new air dam is going to extend my front about 0.3m. The SMART fortwo is just plain DUMB for economy and safety. Just "cute" and easy to park. By the way, it had 55g in the same exact test. I don't know what crackhead decided to put its picture on their page for the 5-star crash test rating search page.
Safercar.gov