I've never participated in one because they want people to sign up to different things, like a list of five items, to get it, I don't consider those as airdrops, but more like bounties disguised as airdrops. I did find a site that discusses best coins for 2018 and there was like three or four links to air drops, and those asked nothing. However weather or not those coins will have any value, no one knows. I just randomly googled air drops and airdropsmob came up and all the aidrops require signup or follow, or registering at their site with personal info.