Usually my feet because once I feel myself going then Id rather step off (if possible) than hang about waiting to crash to the ground! Although have fallen off on the side of my thighs a lot (at least thats where I always have the bruises), usually when sensitive ned decides to explode and either bolt or bronc, or both!
I usually fall off the left, and land on my shoulder, hip and then knock my head. That said I haven't fallen off for a few years. I like to make a point of staying on, the ground hurts.
Last time judging by the marks on my breeches it was my bum but I don't remember. The time before that was square on the top of my head in the water jump at Scone
I've only fallen off twice since starting back in May, first on the side of my head followed by shoulders. Then the 2nd time on foot and one knee. Looked like I was proposing to the horse!