You could definitely argue a few different things are a sign of the best watches around. Some would search for exquisite movement finishing. Others look to a killer dial.
One thing which has been the mark of a top watchmaker for decades, though, is a tourbillon. Once used to ensure regular, accurate timekeeping in a variety of different positions, the piece is largely decorative these days. Still, that doesn't stop it from being incredibly difficult to master – and subsequently superbly expensive.
