We live in Vegas and have traveled both ways many times.
If you like to get in the RV and DRIVE take 93 to Kingman and on to Phoenix.
If you want to see scenic - Old Rt 66, Needles, Colorado River,Lake Havasu and stop along the way 95 is great. We usually go from Parker to 60 and hook back up with INT 10 into West Phoenix.
Our Rig is 20 years old- well maintained and a V8 460 FORD. The flatter the road the better. 95 is the best and we actually take AZ 95 (not to be confused with US 95) out of Needles to 60 and then Parker Dam.
What ever you choose have fun. Happy Rving.