Our answer is that towing with a hitch is better than with a bumper-mounted ball.
Typically, bumpers are rated to tow around 3500 lbs. It's usually printed somewhere on the bumper, or maybe on a sticker. The frame mounted hitch will have more towing capacity due to the way it is mounted.
Also, most trailers have a towing height of 17 to 19 inches, and bumpers on trucks are usually around 20 inches. If the trailer is mounted on the bumper and the front end of the trailer tongue is high, there may be sway when towing. It is best to install a hitch and use a ball mount with the correct rise or fall to keep the trailer level while towing.