I'd like to say neither are that bad for you, but it'd be a lie sort of. I know after years of seriously abusing/being addicted to benzos have seemed to have a major impact on my mental health. Like it's dumbed me down.
Opiates, my love in life; all I can say is they aren't that great for your liver and kidneys, and although I don't know for sure, I'm thinking they're not so great for your digestive organs. Going days/weeks without taking a shit can't be good