I made one as you know, and I agree thing it's good for is gathering Stars. It's around 30 now.
@ mike: Hard to recommend one. Personally I still think "Chimneys of Mushroom Factory" is my best, but it doesn't get much traffic and lags in the amount of Stars so obviously the general audience seems to disagree. "Chief Wiggler's Icey Cave" has been the most popular of mine, with both most players and attempts as well as most Stars.