I think bounty will be more effective because bounty doing ico and many investors who join and it is clear this will be sold and traded, while airdrop only free coin and very rarely airdrop that can be sold because no one interested with it
And in view of the simplicity in airdrop is very often simply do not pay. If both projects worked out 100%, then of course I would choose airdrop, but for now, bounty with me more honest than airdrop.