What is the best keratin treatment ?

The answer is unfortunately none.

It is just about impossible to know which salon is using genuine products or knocks offs. As of 2018 the keratin companies keep changing names cause their brand have a reputations for not working.

A number of salons in Sydney have resorted to buying google reviews and followers for their social media from IT companies in India to make them look relevant. If a supplier offered me a keratin bottle today I would knock it back, I would never risk using it on my clients hair.

Keratin treaments can change hair colour dramatically as it contains ingredients that fades the hair colour.

The brazilian blowout does not fade hair colour. It enhances it

 Do not be blinded by cheap deals, If they are doing it cheap it's cause the product they use is cheap. It is your hair. Your choice.