Fine, let me start with an example, Say if you want to brand your name then sale/lead generation, of course! Branding will help for lead generation and sales after some times, Then Face book advertising is good choice than Google adwords.
In another way, you already have a reputed brand name, now you want to increase your sales /leads, then Google adwords and organic traffic is better than facebook.
Google advertising is bit costlier than facebook advertising, reason behind is
Search traffic(organic) is always targeted, if an user searched about pendrive in search engines related to pendrive ads will be displayed in search results than any other ads, and also people who may interested they directly buy from it, but in social marketing you cannot target for pendrive , may be you can target as Group( Electronic items) , it’s not only depends on category, it depends on people interests, People who came through organic search for pendrive will be more interested then people who came through social networking, this causes to raise advertising cost more in search engines.
First everybody should understand the difference between the audience who looks facebook/twitter/linked in ads and who see google ads. On social networking people usually come to chat with their friends, to play games and do all the fun activities. Their intention is not to buy or sell any product or service. But on Google people comes to find out something. So google adwords is always targeted one.
I am not saying that Facebook ads are not effective. But first we should understand what we want at the end of the day. If we want likes to your facebook page, hits to the website or branding the name then facebook ads are very good. These also sometimes gives you the conversion but not effective like adwords.
In terms of coupon codes social networking sites, such as facebook, linkedin, twitter offers a free advertsing credit of 50$ initially without any initial payments(just credit card verification is enough), but search engines offers free advertising with initial deposits.
Some Real statistics
People have just invested 20$ on Facebook and same in adwords and seen the response.
Face book Advertising
Website Clicks: 155
Amount Spent: $3.76
Bounce rate –less than 50%
Website clicks: 100
Amount spent: 5$
Bounce rate: less than 25%
Google Adwords is good if your business is selling services or products.
Facebook is a place where you can find most active users all over the time, so you can brand it, make them to like your product; so that we can show our product is good.
My personal opinion is if facebook offers free advertising than adwords, start advertising in facebook , if you are not satisfied then move to adwords.