I actually did this trail in reverse, aka, The Boulder Mail Trail. The trip description provided here begins at the Upper Escalante River Trailhead and ends at the Boulder Mail Trail trailhead. Ours was opposite – East to West.
I would recommend the route we took simply because of the drop into Death Hollow. Well, I shouldn't say simply. The drop into Hollow from the East was beyond spectacular. It was also extremely steep and I would much rather go down it than up it.
To sum up the trail in just a few words I would have to say lots of slickrock, lots of sand, lots of cairns, an incredible view, and peacefully remote.
A couple things to note:
Water - some descriptions of this trail say that water is a problem. There is water in Sand Creek (although it is not very clear), Death Hollow, Pine Creek, and the Escalante. There are potholes throughout, especially in Mamie Creek. If you are used to drinking only out of springs you are out of luck. If you are more brave with your water choices, you will have plenty of water.
Route Finding - the route finding required for this trip is more like cairn finding. We only had to break out the map and compass when we thought we were smarter than the Cairns. Follow the cairns, don't move in any definite direction until you see cairns or a trail, and always assume the cairns mark the path of least resistance through the slickrock sections. Always remember that the cairns are smarter than the hiker.
All in all, this was a great trail. It included all the beauty of Zion without the crowds, traffic, and commercialism.