Flight
This drive is shorter (~3.5 hours). The road is a mountainous, windy road with beautiful views. If you don't like mountain driving or steep mountain passes, consider flying into Spokane. Highway 20 is closed in the winter - take this into consideration when looking it up on gps before mid-June.
Flight
This is the less windy and less scenic option. It's about a 4 hour drive, flat most of the way, and very easy driving. Would recommend if not interested in mountain pass driving.