Exeter and Andover have different “feels”. My D, with the enthusiastic agreement of the family, chose Exeter over Andover, and has been completely satisfied with the choice (and her college choices). She has been very happy there.
It really is about fit. Exeter felt warm, welcoming, and transparent to our family, and she felt more comfortable with students and faculty there. They are both great schools, and if you have the good fortune to choose between them, go visit and choose for yourself.
I sense Exeter is getting bashed a bit here, and just want to mention that the Exonian article linked in post 18 above points out that the yield is usually 1:1 (evenly split) between Andover and Exeter, as it seemed to be 4 years ago when my D was choosing. Because it tilted 2:1 in 2014 for unclear reasons, the article was news. It will be interesting to see what happens in 2015.