Depends on the situation, and sometimes what I feel like.
If I'm in a car park where there's no barrier between my car and the one directly behind, I'll back in. I'd rather they nudge a rugged steel towbar than a painted plastic bumper.
At home I usually back in so that the front porch light is shining directly on the drivers side door (none of the other doors have an external lock).
Finally, my car is a large sedan so it's usually much easier to back in. If I go in forwards I usually need to do a quick reverse-forward correction so that I don't swipe the car next to me. Same with coming out, if it's a tight spot then I usually need to do the same... if I'm backed in then I just drive straight out.
I think I've only ever seen one chick reversing in.
