If your goal is to lose weight, it seems like diet coke is the better choice short-term (because it has much less calories) and normal coke the better choice long-term (because according to studies, NSS don't help long term and to reduce their other long-term effects).
So I guess if you drink a coke once in a while, diet coke is better and if you drink coke very often, you should stop drinking coke.
Normal Coke is probably worse but they're both horrible.
I only drink normal Coke but sparingly. Usually I'm having water or plain black coffee. I think the takeaway is that diet Coke doesn't allow you to train yourself to enjoy normal sweet foods again. I just had an apple and strawberries and it is basically candy to me.
Edit: I have a question. Rank these food items by how healthful they are:
> Rank these food items by how healthful they are:
Are you considering mental well-being as well, or just pure physical health? Because in case of the former, option b) will end up with the lowest score.