They have been repaving I-40 between Kingman and Flagstaff which has been rough in prior years. Not sure whats been completed but the areas I've driven recently in AZ have been fine.
I prefer I-40 as its far more scenic. There is a moderate grade from Ash Fork to Williams AZ then lesser grades most of the rest of the way.
Snow is rather rare in the Williams/Flagstaff area in Late March. If weather is clear, I-40 is the easy choice. Scenic and lots of great places to stop and explore as well as far lower traffic. I-10 is just too boring! El Paso is a mess to drive thru!!