Where to find the best smart contract auditers? In here, upwork etc?
You are in the right place, at least on this forum. Do consider posting your future requirement here :
JOBS & SERVICE REQUEST BOARD (Post Hiring requests HERE) You may also want to try out sites like
Xbtfreelancer or
Workingforbitcoins or
Ethlance or you can also try Linkedin.
IMO, At Upwork or Freelancer you will find freelancers that would overcharge you for a not so good result output.