Actually, I have more problems backing up a 5th wheel trailer then I do a bumper hitch trailer.
But, not all of the 5th wheels seem as bad as others. My brother once had a 3 axle livestock 5th wheel and I simply could not back that thing up. When going around a curve backing up it would get stuck in the curve and the only thing I could do to get it to straighten out was to pull ahead and get the truck straight with the trailer again. It didn't help that my older (and thinks he smarter) brother was yelling at me the whole time because he said I'm not supposed to do it that way. He would also freak out if I would look out the window backwards to see exactly what was going on. According to him you are ONLY supposed to back up by looking in your mirrors. I just gave up and let him do it.
Now, there are other 5th wheels that I don't have as much trouble with.
I think that it has something to do with the distance from the hitch to the center pivot point on the trailer and the length of the pickup or something like that.