IMO,most of these airdrops are worthless because these tokens are just being distributed to the communoty to gain exposure to the public,to be noticed or simply for advertisement.If most of the people knew about the project there will be higher chance that these projects will get the support of the community causing most of the investors to join its ICO sales,but if we are talking about those projects that has been with airdrops and doesnt have any plan to have an ICO morelikely these tokens wont have any good value in the future,so most of these drops would be worthless! Bounty campaign is indeed much better to do because you could earn a lot of tokens which can cause hundreds of dollars each in just few months.