I drink tea because I like the diversity of flavours, aroma and energy each tea has to offer. There is such an array! However, I am repeatedly asked to describe the caffeine content of an average cup of tea. There is no sure answer to this question. The reason is that each tea is different from the next with regard to its chemical components. The kind of tea, processing methods, growing region, soil type, climate conditions, even the time of year the tea is harvested could have an impact on any given tea. All I can say is that there is significantly less caffeine in the average cup of tea than there is in the average cup of coffee (by the way, it is also difficult to determine an exact amount in a cup of coffee for the same reasons!).
There is one exception to this rule (and a rather nebulous rule it is!). Good, vintage, aged, sheng pu erh tea apparently has no caffeine in it. Studies in the UK have determined this to be the case. Some people suggest it has something to do with the fermentation process the tea goes through, but a fully fermented tea (i.e. black tea) still has caffeine, so this theory doesn't hold water for me.
A note on anti-oxidents. Yes, tea is high in antioxidents. All tea of the camellia sinensis tea family (basically all tea except rooibus and herbal teas) is jam packed with these little goodies. Antioxidents are excellent for maintaining good health and more and more studies indicate there are more and more health benefits to ingesting antioxidents. That said, we cannot get caught up on the nutrient/chemical composition of the tea.
So the general rule? Enjoy your tea as the Chinese enjoy it. For the whole tea. Not just for its chemical composition and nutritional value. Yes, it's healthy for us, yes, there is some caffeine in most of it, but as with most things in life, it's better to enjoy the tea for what it is than overanalyze its individual components. Smell, drink, feel. That is the essence of good tea enjoyment.