These are two different animals. Both have pros and both have their own cons. In terms of effectiveness, Google edges Facebook no doubt. However, if you are on a mission to build up your social presence, then Facebook is a better platform.
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.
It depends on individual. Both are the effective medium of marketing now a days. Google adds are more effective when it comes to the point where you would like to reach to professional platform then Google add is more comfortable.
When you are marketing on Facebook then you used to get number of people as visitors and some of them are targeted visitors.