With family in both Redding & Temecula, we've driven both many, many times. We prefer 99. Both had patches of road that were horrible & other stretches being repaired last time we used them. We do tend to somewhat alternate between them. I find no significant difference in the difficulty of driving one as opposed to the other. 99 is virtually flat. 5 tends to be more in the low level foothills, so our coach spends a lot of time downshifting which means I turn off th cruise control. I will share this. We practically always spend a night in Flag City RV (Passport America) on 5. Then take 12 over to 99 to avoid both the construction & rough roads south of there on 5. We use 58, as I suspect you will, out of Bakersfield. If we feel like a good meal, we stay at Bakersfield RV Resort & have dinner at there on site restaurant after a dunk in the pool & jacuzzi. If not we usually stay at Orange Grove on 58, just to the east of Bakersfield.