In my view the most interesting art museum in the Miami area is The Wolfsonian.

The Wolfsonian is located in the Art Deco district of South Beach and the building itself is worth a visit. If you have any interest at all in art and design it is also worth going in. The collection consists of all manner of objects from 1885-1945 designed to illustrate how art and design have impacted our lives from the industrial revolution onwards. I think it’s fascinating and you can find something new every time you go.  http://www.wolfsonian.org/