7 days is plenty of time to take both. That being said, context means a lot and if you haven't finished going through FA, Uworld or have glaring weak areas, then obviously your time would be better spent elsewhere. I don't know if 1 is better than the other per se, but I would recommend NBME 16 closer to exam day due to the similarity of the question style. One could probably get more overall utility out of UWSA2 due to answers for every question, but even though UWSA is relatively representative of exam difficulty, the question style will be most similar the the NBME, so if you're only going to do 1 I'd say go for NBME 16.