Just for fun, I drove the full loop around the Estrella yesterday, to compare both road conditions and driving time.
From the 60/I-10 junction in Tempe, the trip from the south is 10 miles shorter than from the north. It took me 5 minutes less time on the south route too, so mileage matches time pretty well.
Despite the extra few minutes, I think that the better driving conditions are from the north side. There are 8 miles of dirt/sand road via Riggs Road, but it is generally quite smooth and a sedan with a good driver should be able to do it just fine.
The south side drive has 9 miles of dirt, but the first four of those are graded to near pavement quality. Unfortunately, the next 5 miles are under the powerlines and perpendicular to the topography, so the road crosses endless annoying little drainages.
Riggs Road parallels the drainages so while sandy, it is smooth most of the way and driving faster.
So if you drive a sedan, the only option is to come in from the north. For high-clearance drivers, the route you take should depend on where in the valley you are starting from, traffic conditions on I-10, and what kind of dirt road driving you would rather drive.
BTW, Google puts the drive time at 1:15 from the south and 1:30 from the north. I was able to shave 15 minutes off each of those, but ymmv.
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