Since the release of iPhone 5S in 2013, Touch ID has changed the way we use our iPhones. It's used to unlock the device, store passwords, and pay for goods via Apple Pay.
Touch ID is a known, proven entity. I've owned an iPhone X for nearly four months, and Face ID works well most of the time — but as Business Insider reporter Tony Villas-Boas points out, Face ID is less reliable, and not quite as fast, compared to Touch ID.
Mind you, Face ID is very good. Apple says it's less prone to being tricked than Touch ID, and can work in most situations where you think it wouldn't: in the dark, if you add hats or glasses, or if you make actual changes to your face. I recently shaved my whole beard off and Face ID had no problems recognizing me.
Still, Touch ID is comfortable to use, works almost instantaneously, and doesn't require you physically look at the phone. Face ID has a ton of potential, but Touch ID is still the gold standard.
Source : http://www.businessinsider.com/apple-iphone-8-vs-iphone-x-2017-9