favorite art galleries in Rome

I'll have a day to visit one (or maybe two) of the smaller art galleries/museums in Rome. I'm debating returning to the Borghese or Galleria Doria Pamphijli (sp?), both of which I've visited before. Or maybe G Colonna or one of the other smaller collections that I haven't previously visited. My interest is International Gothic and early Renaissance. (I'll have two days at the Vatican Museums, so that's not part of this time; and I've visited them many times before.) I'm interested in your favorite smaller galleries/museums in Rome, and would love to know what makes it a favorite