I just switched from a 2 axle patio hauler, to a 3 axle.
I really can't tell any difference. The tires that are on the 3 axle are old, and the shoulders on both middle tires is pretty warn. The dealer said that tire gets scuffed sideways more.
I've had other dealers tell me that some brands go 3 axle because 3 5200 lb axles are cheaper than 2 8000 pound axles, and others say it is better to have 3 sets of brakes.
Anyway, I think both are fine, as long as they are within their load rating.
When I ran the rig over a cat scale, totally empty with empty tanks I got 6,440 on the rear axle, so I would imagine rear axle weight would be the limiting factor with a single rear wheel.
Dodge Ram dually laramie 4x4 w/jake, B&W, Brakesmart.
Kit Patio Hauler 394F toyhauler 5th wheel
Camo 680 Rincon, Green 500 Foreman, Blk twincam Roadking