All tea comes from the same plant, Camellia sinensis.
The taste, appearance, aroma and texture of Tea is like wine or whisky in some regards. Like wine it varies with the region where it is grown, like whisky it can be blended or had as single garden unblended tea.
Tea leaves are typically picked in first, second and third flush. i.e. first leaves of the season, second leaves later in the year and so on.The texture, colour, liquor and flavour of tea are typically what one considers when evaluating or tasting tea. These are a function of the region where the tea is grown, the time of the year (flush), the amount of rainfall, the amount of sunshine and the manner in which the tea is treated after being picked.
So, not all Darjeeling tea for instance, is the same. The first flush of whole leaves will be much dearer than say the fannings (dust) of the third flush from the same tea garden.
We recommend keeping some of the First flush whole leaf teas at your home whether it is Darjeeling, Assam, Kangra or from any other region in the world for a true experience of drinking fine tea.
As a guide, the highest grades of tea are referred to as 'Orange pekoe'. You may also find some teas which have FTGFOP or SFTGFOP on the label (Fine Tippy, Golden, Flowery Orange Pekoe and Super Fine, Tippy Golden Flowery orange Pekoe) these are the highest and finest grade of teas and are truly excellent to drink.
The brewing of the tea is just as important as everything that happens before that. So do read the label and make it just so.
Enjoy your cuppa!
Some interesting pages and facts:
http://www.pinterest.com/totalsuperstore/amazing-facts-about-tea/
http://www.tea-garden.eu/interesting.html
http://listverse.com/2013/11/12/10-absorbing-facts-about-tea/