It always amazes me how people buy cars almost planning to have an accident in them! Think positively, there's only a very small likelihood of having a serious accident, and if that still scares you, you should probably move into the lead-lined bomb shelter now
Remember that even if a car is rated well in crash tests, there's still a significant chance that the occupants won't survive or will suffer sever injuries just due to the shock of the impact, and likewise I've seen hideous wrecks of older, 'unsafe' cars in which the occupants survive. I'm not saying old cars are safe at all, only that whether in a safe car or no, there's no guarantees of survival! I rolled in a 205, which is made of recycled biscuit tins, and not only are both my girlfriend and I here to tell the story, but we escaped utterly unscathed.
Anyway, NCAP don't test backend shunts so I think it's impossible to say which car's going to perform best. We can assume that any car which does well in the front/side impact tests and which doesn't suffer from A-pillar crumpling must have a strong passenger cell and would probably do OK in a rear impact too. However, there's practically no rear crumple zone in a typical hatchback shape, and something's got to give, as they say... If you're worried about rear impacts, just buy an old transit van which has 3-up seating in the front, then you've got a massive rear crumple zone