I'm not one of those who've fished a lot of small water. But when I was growing up in Colorado I fished a small stream named Soda Creek. I caught Brook Trout there that were so big none of the locals I showed pictures to believed they were Brook Trout. I had one that went an easy 5 pounds. I'm sure there are still fish like that there because it is now in the middle of a ski area and golf course. You can't fish there anymore, so the fish are safe to just get big. I had a small lake not far from there that was another "can't fish here" spot with a real dark green and red strain of Cutthroat that were just gigantic. Probably still no fishing there either.
If big isn't a disqualifier, then the Rainy River is by far. If I told you all the stuff I've caught here this year, you would think I was telling fish stories.