Both have a purpose, keeping in mind that they are different target markets.
We use Facebook Ads for our clients that are selling impulse items, toys or clothes.
We use Google Ads for people that generally are doing a little further research.
Both are great for retargeting. Nothing beats Facebook in terms of grainular marketing as the user literally gives you everything - birthday, friends, favorite music, favorite stores etc. This is a treasuretrove in marketing!
All the depends on the target market and the purpose of the advertising.