5th wheel vs. trailer
Gary did a good job with his answer but in more detail, the pivot point with a TT is at the ball which is maybe 4ft behind the tow vehicles axle. This gives a leverage effect for both side-to-side (sway) and up-and-down (bounce) movement. Both cause stability problems that must be controlled or minimized for a safe rig. In addition, how much control is needed can vary as the load in the trailer varies from day to day.
The hitch for a 5th wheel places the pivot point directly over the truck axle and eliminates both bounce and sway. However the point is about 15 inches above the axle that does act as a vertical lever on the truck's frame. During braking, more weight is applied to the front axle and during acceleration, weight is removed from it.
The big negtives with a 5th wheel are more wind resistance, you must have a pickup truck and restricted use of the truck bed. Higher cost and weight for a 5th wheel is typically pretty small when calculated based on actual living area.
If you hook up a 5th wheel incorrectly, it will fall on the truck bed rails and you won't get on the road. If you hook up a TT incorrectly, you may not find out until things go bad at 60mph.