Google AdWords is flexible because it has customizable options for your campaign to suit your particular needs. Google is constantly improving AdWords because it’s one of its primary sources of income.
Facebook’s Custom Audience features are virtually unrivaled by any other social medium. Facebook users build a fairly comprehensive profile about themselves when using the platform, and this can all be used to fine tune your target market.
YouTube is all about the targeting. Unless your video ‘goes viral’ – and very, very few do – this is the place to target small numbers of highly-qualified people with a specific message.