For me Whitney via the Main trail takes 2 to 2.5 hours longer to do the round-trip than do go from the South Rim to the North Rim via South Kaibab/North Kaibab, and that's with the side trip to Ribbon Falls on the North Kaibab trail. Whitney also feels a lot harder because of the higher elevation.

If you do the hike, don't miss Ribbon Falls - it's just a short hike from the main trail and it's really beautiful.