Normal coke is full of sugar which will make you fat.
Diet coke is even worse because all that caffeine will give you adrenal fatigue, shrink the muscle's you do have and deposit it as fat on your mid section.
I hope you are pissed off, enough about this to quit coke.
I completed step 1 yesterday and bought a pepsi. Step 2 will be to quit drinking soda alltogether.
Quitting has to be the goal, neither of those drinks are good for you.
Every morning I have been mixing lemon water and Apple cider vinegar into a liter of water with a sweetner and leaving that in the fridge to drink after meals and I have to say that is a great tasting substiute.
Try it, you might like it too.
I see the future in my house. My wife standing in the kitchen with a new juicer of some kind. Me, drinking liquid beets.
Your right of course about quitting. I quit smoking and drinking. Quitting something hardwired into my brain and body through a couple million years of evolution should be easy by comparison.