I had thought of saying Pippa Middleton's, but that's only because hers is the only bottom I've heard any mention of in the media. In the end I didn't as, while I was sure it was very nice, I couldn't honestly recall if it was really my kind of bottom or not. I checked when I got back in, it isn't - not big enough. Further research on the matter revealed what my answer, had I been paying more attention, should have been: Christina Hendricks.
Happy New Year.