I think you’ll/he’ll know when you visit. Two different schools including the locations. At Carlton one can cross register with St. Olaf, while at Haverford you can do that at BMC and Penn. Haverford is a lot more sporty with tons of soccer and lacrosse fields.
Does he want it to be really really cold (but a dry cold) for several months of the year or be not quite so cold but damp a good deal of the winter? Both school have beautiful, picturesque falls with colorful leaves like in the brochures. Both are close enough to a large city to be able to fly there, to get to professional sports and concerts, to attend events at other schools.