Which is better for rainy trail runs?

The XA PRO 3D GTX. Its GORE-TEX membrane and contaGRIP outsole are made for wet, rough ground. The ACS Pro M has no waterproofing and a street tread.

Can I wear the XA PRO 3D GTX as an everyday shoe?

You can, but it is heavy at about 14 oz and the GORE-TEX runs warm. The ACS Pro M is the more comfortable casual pick.

The XA PRO 3D GTX is built for abuse, with a protective chassis and a lugged rubber outsole. The ACS Pro M is a lifestyle shoe and its faux leather upper wears faster with daily street use.

Is the ACS Pro M good for hiking?

Only on easy, dry paths. It lacks a chassis, deep lugs and waterproofing, so it is not suited to rocky or wet trails.

Does the 12 mm drop matter?

It gives a more traditional, stable feel and suits heel strikers. Runners used to low-drop shoes may find it high.

Does the ACS Pro M fit wide feet?

It is a standard-width sneaker with a textile upper that gives a little. The XA PRO 3D GTX runs true to size with a roomier trail fit.

Salomon XA PRO 3D Gore-Tex Trail Shoes vs Salomon ACS Pro

Buy the XA PRO 3D GTX for wet, rocky trails and long days on your feet. It has a GORE-TEX membrane, a 3D chassis, a 12 mm drop and a grippy all-terrain outsole, and owners rate it 4.5 out of 5 across 133 ratings. The ACS Pro M is a lifestyle sneaker with no waterproofing, a softer street look and a narrower size run, so it suits casual wear rather than mud and rain.

Choose the XA PRO 3D GTX if you run or hike trails in wet weather and want grip, foot protection and a stable ride.
Choose the ACS Pro M if you want a Salomon sneaker for everyday wear and city walking and do not need waterproofing.

Prices

Salomon XA PRO 3D Gore-Tex Trail Shoes: $102.00 at Huckberry (checked today)
Salomon ACS Pro: $89.55 at One Block Down (checked today)
Difference: the Salomon ACS Pro is $12.45 cheaper than the Salomon XA PRO 3D Gore-Tex Trail Shoes today