Which porcelain veneers are the best? Which dentists use these labs?
Lots of human hands involved with dental lab work. Commercial labs vs small independant labs vs in office lab or CERC 3D...it is all in the control of the dentist you choose and the dental material (porcelain or eMax or CeraSmart) they decide to utilize and characterize. It can also be limited to finances, are you paying $2,500 per veneer or $600 per veneer....small highly cosmetic labs charge the dentist a premium and dental plans would rarely cover any of that expense.
That is a difficult question to answer. There are many very skilled lab technicians who are true artists. Do your research on the dentist you are considering and ask to see before and after photos. Get the name of their lab and research them also.