I've had the most enjoyment from the Sand Kingdom. Also, there's a lot of Power Moons really close to each other in the town (three from planted seeds, one in the roof, one in the fountain, a flagpole that gives out more coins than moons, and several regional coins), so it's really easy to grab a lot of coins in a short amount of time. But there's a lot of room to ride Jaxi, the cacti are always fun to destroy (especially when they make that Super Mario World 2 sound effect), the ambiance does its job by not grating your ears by 5 minutes, and I like the contrasting ice underground areas. I think I've spent most time in the Sand Kingdom compared to everything else, just feels like there's more to do. Also, I can make Mario in an inner tube or at least make him cook in a Parka or something.