One of the free City of Paris museums that we just visited in March was the Petit Palais. Absolutely no crowds and lots of great art. There was a Bouguereau Blessed Mother with cherubs that I've always wanted to see, and in person it knocked my socks off.

Nissim de Camondo and Jaquemart-André are in pretty close proximity to each other. Camondo is smaller so perhaps see it first then head over to the other.