We went to Duluth the weekend of the Blues Fest - so basically just for fun and we were torn between two hotesl. We never once regretted our stay at The Canal Park Lodge. It was clean & comfortable. The room had a nice balcony overlooking Lake Superior, and was right in the heart of Canal Park - quite the happening place in Duluth.
Another nice thing about the hotel room was that it had a refrigerator and microwave, so we could bring our left overs (bread pudding) and save it for the next morning.
Canal Park in Duluth are a nice place to visit - it's beautiful and there is enough to keep you busy for the weekend.
Note: We visited in August and the lake water was too chilly to really swim in - it is pretty far up NORTH :)