You could do both for airdrop and Bounty. You could make an announcement for airdrop and fund it with small percentage of the supply and you could do a Bounty campaign for making your project around the social medias. If you are not going to do and ICO then do Bounty campaign. It is proven that Bounty campaigns really help a project gets around people. Also be careful when you are going to do an airdrop. People tend to have multiple accounts to participate in that.