We stayed in Colmar 3 nights followed by Strasbourg for 3 nights in September. We did not appreciate Colmar until the evening when the lights were on and then it was enjoyable to walk around; otherwise, it felt very inauthentic. The best thing about Colmar was the Hop On/Hop Off bus that left from the train station. The friendly TI will have the pamphlet with all the info. We got on at 830 and there were about 7 stops, we chose to go to 4 of the towns: Ribeauville, Riquewihr, Kaysersberg and Eguisheim. We liked Riquewihr and Kaysersberg the best, though liked all 4 more than Colmar. The Hop On/Hop Off bus was an inexpensive and easy way to see a number of places without needing a car. It is ninety minutes between stops/pick ups which was adequate for us, but people can certainly stay longer if they wish.
We really enjoyed Strasbourg! Beautiful city with a river through the center that is really enjoyable to walk around if the weather is nice and it was for us. We spent a lot of time walking down by the river, enjoying the architecture and beauty of the city. Petit France is a place you will want to see. We stayed close to the Cathedral which is in a busy area, but it is very nice and we were happy with the location. I would happily recommend Strasbourg and would gladly return. We also took a river boat ride. I did a search on the highlights of Strasbourg and that's how I came up with what we were interested in seeing.
As we had plenty of time, one day we took the train to nearby Selestat. It was rather worn and tired and a disappointment. I would not return.
I have no restaurant recommendations for Strasbourg, but if you go to Colmar, Adriatico is an Italian restaurant that was recommended to us, and we had a great meal/time there. The place was filled with locals.