Is diet pop bad for you?

I gave up pop about a month ago, and have been doing pretty well since. I used to drink about 44 oz. of a diet pop a day. In the past month, I have bought 2 44 oz. fountain pops, and a 20 oz. high fructose corn syrup-free soda (Pepsi Throwback). I decided to make the change because I felt like it was time to get a little healthier. I just wanted to know if living a pop-free life is better than not. I have been substituting pop with water and mixing juices (not from concentrate!) with carbonated water.