On large pages I've had massive issues with Promoted Posts - flooded with spammy comments that suggested all additional impressions were fake.

Facebook advised Promoted Posts were more effective on smaller pages (eg. <1,000 fans).

I had to mention this just because we're talking about ads etc...

Facebook iOS install ads - ridiculously good conversions on installs, and then active users. Better than any other ad platform that I've tested with.

Facebook unpublished page posts have been really successful for me once you get the targeting down. I've had success with lookalike audiences, as well as with targeting one precise interest + one partner category.

I've tried Facebook ads proper: decent CTRs and good targeting, but I had a poor landing page for facebook users so eventually underwhelming conversions.