Which one?
There's Nate Harrison Grade on the south side. Did that one Friday. (Pro Tip: if you plan on hiking while at the top, dogs aren't allowed on the trails.) That ones pretty smooth. There's a somewhat hairy section towards the top. But overall pretty mellow.
Then there's the High Point Truck Trail to Palomar Divide Truck Trail on the NorthEastern side. Did that one today. It was a blast. But plan a day trip. It's 29miles total (5 of which are paved, but very twisty). 29 miles doesn't sound bad, until you realize you are traveling at 5-10mph for the majority of the trail. But that was the best trail I've ever been on. Tons of views, a few challenges to keep the mind sharp, it was a blast.
I live in Oceanside, so Palomar will be my primary spot.