I would suggest picking up a copy of "Guide to Moab, UT Backroads & 4x4 trails" by Charles Wells when you get to town. I found it to be a most excellent guide for the area. If you go this route you can have several alternate plans in place if a certain trail doesn't work out.
With that said..... I suggest taking the trail to Tower Arch in Arches Nat'l Park. Not very crowded and a most excellent trail.
Have Fun!:greg: