IF both tires are E rated and the load capacity is similar,
towing when properly inflated should be similar.
the 3rd layer of steel thread is to keep the casing UNIFORM which adds to EVEN wear and = more miles.
that's why the A/S is known as a mileage champion.
that may/not matter for towing since E rating = E rating.
the m/s has a newer tread/block design, some of the changes will result in noise differences or traction in water/mud.
rubber compounds may be different too, with the newer tire a tad more grippy but with a bit less durability.
you can READ 100s of reviews of both here, from ALL sorts of users.
Michelin LTX A/S
right now the a/s is on sale, this may be a clue it's scheduled for replacement by something else...
or it's just a sale.
the m/s appears to be the #1 (allseason) truck tire at TR right now, but it's newer
and the longer a tire is available the lower the ratings tend to be. 66 reviews for the ms2 vs 350+ for the a/s
Michelin LTX M/S2