Mine is the four corners regiona little extended because it has to include Moab but that's probably not four corners proper, so basically like if you stood at the Four corners monument and did a square milage of like 400 miles in either direction

. There is just so much diversity, different types of desert to the high alpine above treeline of Colorado to grasslands of n AZ and NMand of course the canyon country of Utah.
20 years ago I would've said the Pacific NW region and while it's beautiful imho nothing can compare to the Four corners