Care to expand on how or why solids are preferred? In practicality either will work. I'd be more concerned with axle wrap and a ball hitch. I think brenndatomu is on track with the leverage on an axle, hanging too far out. But the ball with allow some pivot/reduced fulcrum. Mounting forward of the axle on the frame will increase safety (flip over backwards) and weight carrying much like a fifth wheel. Or just moving closer over centerline of the axle will help.
A tow/ hitch point on the axle is preferred on a quad. IRS with the frame hitch loads the rear suspension and takes away grip from the front wheels, which need to be driven wheels as well ( 4x4) to get maximum grip, which we all know it's the limiting factor when hauling heavy stuff like wood with an ATV. Steering is also a good thing too.