I'm talking about coffee and tea here, and some people are going to say - "Hey - that acid rots your teeth." That's not what the research says. A study in Japan found no correlation between drinking coffee WITHOUT SUGAR and tooth decay. It's the sugar that rots your teeth.
Think about the different teas. There's red tea, green tea and what's called oolong tea, which is something halfway between red and green.
The healthiest drink in the world is green tea - healthy in many ways. There's even reason to believe that - without any sugar - it's good for your teeth, fights cavities.
If you like to sweeten your tea, I'm inclined to think that the best sweetener is stevia, a product from a plant that's very sweet, with no calories. I don't know of any concern about health hazard, but to be on the safe side, I wouldn't abuse it. There's a lot of different stevias, and some taste better than others. I prefer the NOW brand, which is hard to find in stores but sold by Amazon.
Personally, I think oolong goes best with a meal.
If you want to do it right, don't use tea bags. Get loose leaves or green tea powder and learn how to brew. This takes some time, but it's worth it. You'll never go back to bags.
If it's not abused, coffee is a very healthy drink. Be careful with all that caffeine, though. Think about decaf, which has about as much caffeine as cocoa - esp. after the morning hours. No sugar AND none of that artificial creamer. which is just corn sugar. A little milk in your coffee won't hurt you.
Edit - I have been asked to provide a link to show that unsweetened coffee was not shown to harm the teeth in a study.
I have to admit that at the moment, I can't find the study. However, I can link readers to a dentist who says that COFFEE HELPS THE TEETH BY FIGHTING CAVITIES. The dentist says, of the various health benefits, this is the best.
http://www.webdental.com/profiles/blogs/coffee-can-decrease-tooth-decay
Edit - SORE LOSERS!