Rowher Flats is the best place to start wheeling in my opinion. It isn't half as crowded as Hungry Valley and everything there is more Jeep friendly where Hungry Valley is more for quads and motocross. I can't remember the exact name of the trail, but if you run "The[something] Truck Trail" starting from the gate off Bouquet Canyon, it's pretty steep and a lot of fun. For first timers, I would recommend that trail, but starting from the staging areas inside the park and finishing at Bouquet Canyon. Then if they are feeling adventurous, turn around and go the other way.
JK-JEEPER, I was planning on working on my Jeep this weekend but if you would like for someone to show you Rowher Flats this weekend sometime, PM me. I would be up for heading out there. It doesn't take too long, I think the longest you can spend out there without doing all of the trails twice is about three hours. My parents live in Castaic, and I am overdue for a visit. If my dad is home, he would be willing to come out with his Jeep too.