there is no "best", it is all down to personal taste . If however you mean what the most widely prized is, that is a different matter.
For coffee most people think that Jamaican Blue Mountain is the best ,widely available coffee and this is certainly reflected in the high price. In my local shop its about 4 times the price of a sumatran or kenyan coffee.
As for tea, again it can be a matter of taste. However usually a single estate, first flowering tea is the most rare and expensive.The tea is graded on the height it is picked at, how much of the tip of the tea plant is picked etc. For the best place to find out about really good quality tea and coffee (rather than a palce that only specialises in one or the other) try the website for that lovely London shop Fortnums& Masons. I go there once ayear and manage to spend a fortune every time!