The majority of the crowd that arrives at Sunol Regional Preserve head towards Little Yosemite. Some of them proceed on that miserable trail to Rose Peak. If there is a better character building trail than Rose Peak, I am yet to see it.
The sensible folks, however, go in the other direction towards Flag Hill.
This is one of the trails that goes up Flag Hill but comes back down in a gentler loop. This is my Strava recording of the hike.
https://www.strava.com/activities/4910458652. You climb about a 1,000 feet in the first 1.3 miles to the summit of Flag Hill. In places, it is exceptionally steep and feels like proper mountaineering, particularly if you are coming down. I wouldn’t come down from Flag hill in that section. I have done this hike twice clockwise from the visitor center parking lot and it is much better that way.
It has some absolutely stunning scenery and almost no one else on the trail.
From the summit, you get a sweeping view of Calavaras reservoir and Sunol Wilderness.
On the way back in the gentle downhill, you run into High Valley Camp.
This is a comfortable 4.2 mile loop, that you can do in about 2-2.5 hours. Highly recommended to do around sunset time in Spring when the colors pop.