We really enjoyed the free walking tour. We booked through freetours.com and it worked out very well. Our guide, Nodo, was very knowledgeable and did a great job in summarizing all the important historical and political points without being boring :D Georgia has a long history and it's shown all over the city. It actually sparked my interest to read more about the history and politics in this area of the world. He also talked about Georgian culture and gave recommendations for all kinds of things (restaurants, shopping, sulfur baths, pubs, etc.). Needless to say, I can highly recommend going on one of their tours!
BTW, even on a sunny day in winter it is a nice thing to do ;)