If you fly a lot and you worry about these things, and even if you don't, here's the data. Your odds of surviving a plan crash are:
49% in first class
56% in the body of the plane
69% in the back of the plane
I anticipated it would be safer in the back, but it is nice to have confirming data. It is surprising though that the difference is 50% compared to sitting in first class. You would think at hundreds of miles an hour it wouldn't make that big a difference.