We dabbled with Airdrops and giveaways but there was an enormous amount of bots participating and it wasn't useful to us.
How about a proper bounty campaign? One that would include twitter, facebook, creative content campaign (youtube, blog posts, articles), and a signature campaign.
In order to eliminate (or greatly reduce) spam and bots, don't run the campaign on your own. Hire an experienced bounty manager. I've worked with some of them who have zero tolerance for spam.
I don't see much use of airdrops. I personally rarely take part in them. There is too much noise, with little or no real promotion for you.