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.

> But if I have to choose between diet and normal coke

no one has to make that choice