All of the prebottled tea you'll find at a store contain either sugar or artificial sweetener.

You can buy individual tea packets that you steep in hot water, which is the healthier option. (Don't get lipton tea bags, it taste like shit)

I personally love bitter drinks, I drink espresso black, but I wouldn't recommend you move from soda to black tea. Get like Earl Grey or a white tea, both of which taste great on their own.