Tell us a bit about your interests when at a park. Would you like to hike some? a lot? or, do you motorcycle to the overlooks and keep moving?
For instance, Grand Canyon is worth one day if you don't hike. Several if you hike.
As others have suggested, pick a region and stick to parks in that region. If going to the GC, I'd get in Zion, Bryce, Canyonlands, Arches and save other destinations for another trip. Or, go the northern route...but you can't do both.
Check out the trip report in my sig to see what a Southwest loop could be.