Rainbow Road
Wario Stadium
Block Fort
Toad's Turnpike
Fairly easy imo. Rainbow Road is the final level, Wario Stadium probably has the most iconic fairly easy shortcut (besides rainbow road). Block fort is the signature multiplayer map. Toad's Turnpike was the only one I thought about, and picked it over a few others due to the cars.
Casual Revolution 2007 - 2015
Casual Double Down 2015 - ??