Considering that Facebook now has more visits than Google it is surprising that Facebook advertising is still considered inferior to Google advertising.I have no figures on this but the price of Facebook advertising compared to the price of Google Adwords indicates a much lesser demand.
The factors that should push you towards Facebook Advertising are
The cost - as I've said the cost per click is much less than on Google.
The traffic - not only does Facebook traffic now exceed Google, the length and therefore the quality of the view is greater.Many now use Face book Direct messaging rather than email and consequently have their Facebook as their home page.
The ability to precisely target.Google adwords have the disadvantage of displaying to all and appearing at the top of the search page where all your competitors are also advertising.This may be partly overcome by joint venturing with your competitors but in certain markets that could be illegal.
Facebook on the other hand will be displayed only to a defined audience.
Basically you can choose on Facebook what sort of person you want the ad displayed to. This can be by gender, country, locality, age, date, interest(really be detail of individuals bios) You can therefore be certain that only interested potential customers will see and therefore click on your advertisement and that conversion will be much greater.
The other massive advantage it has over Google is that it carries photographs or graphics and therefore is far more interesting and attractive.