I prefer Facebook ads right now as I can select an area, age and any interest I want. If someone were to theoretically write a book “How to really be prepared for your mission” about the need to study the anti material so you can speak to it when you are out, using Facebook you could target only 17/18 year old boys who list LDS and live within 250 miles of SLC. They would be the only ones who would see the ad for your free Mission prep ebook. If you have a bike shop you can hit just people in your town who list biking etc. Google does not offer this type of granularity.
The internet will be the end of all this madness. Google ads probably cost them $1 per click. If you click 10x when one is served they aren’t charged but if you click once on every ad you are served they will be charged each time I think. I have been using them for 5+ years.