I’ve used both, @albertmora- although definitely more on the Facebook ads side.  I think they are different in that people aren’t searching for something to buy on Facebook.  So I think Facebook ads word better as a list-building tool where you are directing people to an opt-in for a freebie. 

I have a free e-book that I wrote for Hubspot here on Facebook ads: http://www.hubspot.com/how-to-create-epic-facebook-ads/  It’s a little out of date, there are newer types of Facebook Ads that have come along.  But the general principles are still the same in it. 

There are different group of customers:

Group #1: People who are in need and searching for itGroup #2: People who need but are not searching for itGroup #3: People who will not buy from you in next 6 to 12 months 

Now every business have different % of target customers in Group #1 and group #2, whether its B2B or B2C …

Now social media Ads (FB or any other) is basically interrupt ads that works for Group #2 (Focus on Sales) …. and also works for Group #1 to become a known company (Branding) … Or to refer friend (Social Referral, very cool)

For us, many a times FB ads have worked really work … Google ads almost works …. cost wise, sometimes FB can be really good … in recent times we are shifting more to Google as FB is becoming expensive … thanks!