I love the prospect of going to the least popular items on this list. The volunteers sound super passionate and not having to fight lines is wonderful.
I've recently come to love going to the hyper-local, out of the way, or seemingly forgotten museums. Their collections are often unique and sometimes quirky. Most of all, though, I find that it's far easier to connect with the history of the place that I'm visiting because the museum is more intimate and the collections more accessible.