Depends on your definition of "unknown". Unknown to whom?
If you mean that the tailor is not known to the world at large, or even to a smaller subset of that; the English speaking fora, then it is not surprising that they are "unknown". After all there are hundreds of tailors in Italy, and the better ones are generally 'known' to the locals of the city/town where they reside.
Many of the more known ones have an established history such as Caraceni or Rubinacci (btw, I hope that people realize that Mariano is NOT the tailor, and that London House has had a few tailors over the years). Others are fortunate enough to have had famous international clientele and thus have had their reputations more publicised. Does this mean that only these 'known' ones are good? Absolutely not. Does it mean the smaller, more locally known tailors are: as good, better, worse? It depends on the tailor. However, with the more 'known' qualities, you are paying for an established look and expect a certain level of quality. While on the other hand, with the smaller, local tailors you are taking a risk based on how you chose the tailor, who suggested them to you, how well you can judge workmanship and cut, etc. That is why this undertaking would be more risky.
It also depends on what you mean by "best". What is 'best' for an American audience may not be 'best' for a certain region in Italy. How many in Rome would consider a neapolitan coat (as stereotyped on many English fora) an ideal business coat? How many in Napoli would consider the more columnar, sleek Roman style the epitome of a suit? What would the northerners consider either cuts?
That is why there is no "best", and the "unknown" question is a red herring.