I've had several of both in my business. Bed length had nothing to do with ride quality. Some long beds can ride worse than some short bed trucks. Wheel base and suspension packages and the load on them has more to do with ride quality.
A long bed isn't necessary unless you just want one.
Some points;......
Some new 5th wheel trailers have the rounded/notched front corner profile that eliminates the need for a sliding hitch.
The Reese Sidewinder pin box replacement works with a std 5th wheel hitch and short bed trucks.
The Andersen hitch system eliminates the need for a slider.
And of course the holy grail of auto sliders the PullRite Superglide auto sliding hitch.