Benin or Niger if I have jjust 3-4 days?

In December 2014 I will go from Ouagadougou to Chad and can do stopovers in Benin or Niger. Any suggestions as to which would be more interesting? We both do photography. I am an anthropologist. We have been to Sudan, Uganda, Cameroon recently and will have been to Mali (with 4 days in Dogon country on our 20 day trip) before this trip.