What's "best" kinda depends on what you're looking for. The other other end of town from the trails that have already been suggested is more open and will give you better panoramic views.
Here is Barlow's map for you. Don't know if you've already contracted for the rental, but you really can't go wrong with Barlow. Great folks, and really long-time serious contributors to the offroad community. They also guide in Moab and on the Rubicon.
And just to keep things bizarre, the picture below is of a guy we met up with on Diamondback Gulch. He was already past the point of his skills to recover when we found him (coming toward us), and was just about to pass the point of no return, as in call the helicopter.
Along with a pink Jeep driver, we managed to convince him he WAS NOT going to like what he was about to drive off of in about 100' and got him turned around. As it was, there was still a hill in front of us he couldn't make it up. I had to drive his Mini to the top of that hill for him and then he made it the rest of the way out.
Turns out it was a rental, lol. I'd hate to see the credit card bill for the month after he got back to Vegas. Turns out he was from Germany and the woman with him was from Austria. It was funny, with wide eyes he kept saying, "Ve have come a vay I tink ve cannot go back."
After I convinced him he couldn't go any farther forward, the woman was very careful to point out that he
was the German; she
was Austrian. It was like the only thing she could think of to put distance between her and the guy who had just scared the crap out of her, lol.
Then when he got out and I was in the car with her, she said, "Ve just kept goink und goink, und it just kept gettink vorse and vorse, but ve tought it must get better. I tried to get him to go back but then ve could not go back." It was a riot.
We were actually late getting the Jeep back to Barlow's because I wasn't about to leave the guy out there by himself. The folks at Barlow's didn't care, they just wanted to hear the story! That was back at the end of March. I bet if you mention a Mini Cooper on Diamondback Gulch they'll know what you're talking about.
Oh, and if you go out on Outlaw Trail, go to the Honanki Ruins. Pretty cool cliff dwellings out there for a very short hike.