Sway control built into the WD mechanism, e.g. the Reese Dual Cam or the Equal-i-zer system, is far superior to the friction type. The primary reason for this is human - the friction device relies on the driver to apply it each time the trailer is hitched, and to set the correct amount of friction, neither too much nor too little. In my opinion few of the friction devices are set up correctly. Folks turn the friction knob enough to get some action and hope it is enough to do the job, but they don't know for sure until it is too late to do anything. And since too much friction often produces noticeable hitch noise at low speed, there is a tendency to go light.
With the WD type, the sway control is in place as soon as you hitch up, and the amount is in proportion to the weight on the hitch. It's automatic and essentially foolproof. And no extra device to store either.