I can’t speak to CWRU and Dennison specifically although I know people who have had good experiences at both. However, as I’m sure you know, the choice boils down to a mid-size urban university and a non-urban LAC. In my family, the preference was different for each of my two kids. My S felt that LACs were just too small/confining and after visiting different colleges, he focused his search on mid-sized urban universities. In contrast, my D fell in love with the LAC experience from the start of her college tours and focused on those. Both attended the right fit school for their interests and personalities and both had wonderful experiences.
Your S has two great options and should be congratulated. At this point it is about finances and fit. If your S prefers CWRU I hope they come up with enough money to make it work.