I'm very late to this post, but wanted to add some more good local info. From Mesa, or the east valley, to get to I-40 heading East, a pretty drive is 87 to Payson as suggested, then east on 260 to Heber. Just past the Red Onion Restaurant (a good spot for a tasty burger, btw), take 277 towards Holbrook. You will have to take a left turn onto 377 a few miles in, and that'll take you to just south of Holbrook where 377 ties into 77. A left onto 77 and in a couple miles you're in Holbrook. I've driven this a number of times in our class C - it is a 2 lane hwy, and has some truck traffic, but I've found it to be the quickest way for me to get from the east valley to hit I-40 and go east. I will say, if you are leaving from Phoenix itself, or the west side of Phoenix, just take I-17 to Flagstaff and take I-40 east - that'll be easier and quicker. My suggested route is for folks in the east valley (Tempe, Mesa, Chandler, Gilbert, AJ etc).
I agree that the drive thru Globe and Salt River Canyon on 60 is pretty, but not for most folks with RV's. Doable, but not my preferred route.
enjoy.