39w2d, although my OB also would have been available at 39w6d.
I chose the earlier date because my mom and step-dad were flying in the weekend before (tickets were booked way before we knew that I'd have a c-section). Since DS was already estimated to be 9 lb 15 oz at 38w4d, I decided to choose the earlier date to give them more time to spend with DS. DS weighed 10 lb 6 oz, so the estimate was pretty accurate.