As a self-described ignorant tea-lover, I don't know whether there is
an official organization that rates teas the way you describe.
However, I believe that trying to rate the "best" of tea (or just
about anything else, for that matter) is subjective. Best for what?
Flavor? Aroma? Anti-oxidants? The first two are definitely subjective,
and the third is too variable to be of use.

Look at it another way: what is the best wine? The one that wins the
most awards? Again, simply too subjective to mean anything.

Like you, I'm interested in hearing whether there is any formal rating
system/organization.

Alan