I wouldn't mind walking with Riley. As from how the storyline goes with him he seems very kind, but at the same time tough. It'd be pretty cool if his Lucario could walk with us as well. Lucario seems like a calm and solemn pokémon and it would be pretty mesmerizing to be able to see him walk with yourself and Riley.
As for Aaron, he seems like the type of guy who wouldn't mind taking a fresh walk with his Beautifly. If he and his Beautifly could be able to walk with you, that would be a memorable sight to see.