It is all about physics and leverage. Tow trailers are at the end of the truck and have more leverage effect the truck than a fifth wheel/goose neck that is ahead of the rear axle. As far as dually's having more stability than a SRW, it is more about sensation/emotion than physics. The truck is effected more on the how the springs are mounted to the axels/frame which is the same for both kinds of vehicles. Assuming that the dually and srw have rear sway bars which is optional on srw. I have driven most and they both are stable with 5th wheel/goose neck trailers.
Backing of 5th wheel is more of a challenge than tow trailers because the of physics again. The fifth wheel trackes differently and responds more slowly than tow trailers. It takes more practice to back a 5th wheel IMHO.