Which DNA test for ancestry or ethnicity is most accurate?

I am thinking to buy a genetic DNA Ancestry test. Which one should I buy?

This is a difficult one. I don’t think they’re very accurate. The same raw data can give you slightly different results, but I would say you can cross-check - take the results from 23andMe or Ancestry or Family Tree DNA and use other free/affordable resources online to read your data further.

23andMe is probably best value, but I read that Family Tree DNA was the gold standard a few years ago.