My vote would go to Kazimierz Dolny
You beat me to it and I was there on Saturday as I only live 5 klms away from there, went to a wine tasting in Janowiec Castle, which is a short ferry ride over the Wisla.
Then in the evening we had dinner in the market square listening to a band and they try to put on something every weekend.
Best weekend to go there is the first week in August as they have a film festival there and there are events and open air showing of films throughout the town, and at the end of the week there is a big dance party in the Kazimierz castle.