Tea is...complicated.
Be careful though, black tea is high in oxalates. Too much of a good thing can be a bad thing. Kidney stones are no fun.
Three years ago...I tossed away the sodas and stuck to unsweetened tea. In an average month...I might drink ten ounces of a soda...that’s it. I admit....I drink probably half-a-gallon of tea per day....but I think it’s a better substitute than soda.
Coffee, OTOH, is a different story. Unfortunately, I need to go decaf, so I suspect I lose much of the benefits of coffee as well.
There are lots of ins and outs to teas. A big unknown is the effect of processing and oxidation on tea’s medicinal values.
One tea not mentioned is fairly new to US markets, as such, called “white tea”, it is processed differently from green and black tea, with the intent to minimize oxidation.
http://en.wikipedia.org/wiki/White_tea
As far as some people getting problems with stones from drinking too much tea, there is likely a genetic component as well. There are at least three major ways stones form, and tea would likely affect only one of them.
The Chinese are currently very strong advocates of strong and frequent tea enemas as a means of fighting colon cancer.
I’ve been a green-tea drinker for many years, and, I have to admit, I have no other explanation for the increasing health I have noticed. Since I haven’t done much else or made many changes in my diet, I am hopefully choosing to credit the properties of the green tea. I drink about 6 cups a day, as my primary hydration, so it’s not a “1-cup-and-done” situation.
Black and especially green tea is full of toxic fluoride. Look it up.
White tea is supposed to be better.