Back to the OP's question and somewhere along the line mention of both types of guns being available for rent; I would suggest that you rent one gun and shoot a full sporty clay course with it. Then come back the next day and shoot the same course, but rent the other gun. That should give your son a better opportunity to judge for himself how each feels in his hands. I would personally find it difficult to form much of an opinion shooting less than a few boxes or by switching the guns between each other over a few targets. I'll also mention that skeet is still the best back to basics shotgun game. Shooting skeet from a gun down start or off the shoulder as one might approach a dog on point is a good way to see how a gun handles.

Let us know how it goes. Great that you are shooting together!