Quick answers: The Michelin LTX M/S is one of the smoothest riding LT tires available with one of the lowest rolling resistance of any tire on the market. Ask anybody who operates a Hunter GSP9700 Road Force Balancing machine. All tires have variations in sidewall and tread stiffness which shows up as variations in rolling smoothness of the tire. Most tires have variations from 15 pounds to 70 pounds in road force when measured by the Hunter balancing machine. Michelin LTX's M/S's rairly have road force variations in excess of 15 pounds. Next ask anyone who has had Michelin LTX M/S tires who has changed to another brand if they saw a change in gas mileage. Most people will say they saw a 10% decrease in gas mileage switching from Michelins to another brand. The Michelin gives a smoother ride and better fuel economy. ST or Special Tire is a designation given to "passenger car" tires which have been allowed to be strengthened by using heavier plys and stiffer construction to fill various niches in the marketplace including trailer tires. The Marathon is such a tire, a modified passenger car tire, designed to run at passenger car tire pressures or slightly above. When new, they do seem to provide a smooth ride and fairly low rolling resistance. Their reliability and durability is suspect.
Michelin LTX M/S durability is often surprising. My sister-in-law who lives in Orchard Hill which is outside of Griffin, Ga. has one of the Ford Explorers which came with Firestones. On the recall, she was given her choice of tires. I told her LTX M/S's. She now has 235,000 miles on that set of Michelins. At 200,000 miles we contacted Michelin to let them know. We got some nice Michelin baseball caps and mouse pads for our effort!