I have very little knowledge indeed concerning tea, and that little was mostly picked up during the guided tours of the Labookellie Tea Factory which I went on, so the views could conceivably be somewhat skewed, although they certainly seemed to be given in utter good faith.
On the subject of the quality of teas it seems that the very best leaves are the two or three at the top of each plant - the newest and freshest of them all. The lower the leaves on the tea plant, the less desirable and the cheaper. The lowermost leaves get spattered and splashed with mud and earth and are considered the lowest in quality too.
Our guide was particularly scathing, I'm sorry to say, about two kinds of tea which you mentioned and which are however undeniably popular: Earl Grey, and all tea in tea bags. The reason that Earl Grey was criticised was that the flavour and scent of the bergamot are so strong that the flavour of the tea itself can hardly be perceived - consequently producers exploit the situation to sell very poor teas at a very handsome margin. Similarly, according to our guide, the tea in tea-bags is to a large extent composed of the lowest quality leaf and the shavings and tea dust which are by-products of the drying and sorting processes.
I believe the very finest qualities of tea come from the foot-hills of the Himalayas in northern India (for example Darjeeling, Assam) and above all from China, which is the country of origin of tea. The plant's latin name is "Camellia Sinensis"
(Chinese Camellia). I have also heard that top tea connoisseurs have nothing to envy top sommeliers in terms of subtlety of palate (no to mention tongue) and that the very highest qualities of the choicest teas command prices comparable to those of highly illegal substances. There is an interesting article on Darjeeling tea here: http://www.teaandcoffee.net/0704/tea.htm
The subject of tea brings to mind a fascinating history which I read a few years ago, not directly related to tea, but rather on the East India Company, which acquired unbelievable wealth for its members and indeed for England as a whole, partly through its dominance of the tea trade. According to this book the American Stars and Stripes flag was a direct copy of an East India Company flag design, with only some colours inverted. Of course there was also a famous party held in Boston harbour over taxes on tea (and other commodities) foolishly levied by the Crown. This book was written by Antony Wild, who is himself a director of the East India Company. It has fabulous illustrations too.
And looking for the above pointer I came across this other book which I'm putting in my wish list too:
With best regards