I don't play daily either, but I do quite often. The 3 courses I mentioned are all widely-praised fan-favorites, and I simply don't get why they are as popular as they are. They aren't bad, they are all actually pretty good, but they are still overrated.
I often hear people praising Waluigi Pinball and Delfino Square as the best courses to come out of Mario Kart DS, but personally, I think that title belongs to Airship Fortress.