I would charge at El Centro - Ehrenberg - Kingman (the new one is v3) - Tusayan. Beware the elevation gain on the last 2 legs is over 3,000 ft on each one.
The other reasonable option would be El Centro - Quartzsite (Ehrenberg would also be fine here) - Wickenburg - Tusayan. This one is slightly inferior imo because the last leg is a lengthy 185 miles with >4,000 ft elevation gain. Not impossible by any means, but not easy either and you'll be charging to near full on a slower v2 in Wickenburg.
Lastly, I just noticed that staying on I-8 longer and then cutting north through Gila River isn't that much slower so that would be an option too. This one is almost all interstate highway so while it's similar in how much time it takes, it's more miles which means a little more charging. You also skirt PHX metro on this one which could mean hitting some traffic depending on what time of day or day of week. There are many charging options on this route but the general idea would be to drive San Diego to Gila River, then skirt the NW side of PHX metro and head up to Flagstaff on I-17. I personally wouldn't choose this option unless there was a weather consideration or I had someone to see or something to do along the way.
If I were you, I'd pick one route on the way there and another on the way back to make a loop out of it and make it interesting. There are many options that are all within an hour of one another. Either way, it's going to take 10-11 hours one way including the charging.