It is really hard to tell as there are so many scam airdrops.Most of them really are scam.You can rarely find a single one that is legit and going to pay you right.To find the right tokens and stay away from scams, go through the reviews in the forums about the Airdrops. Study about the team and the business plan.If you want to participate in any airdrop make sure to check if that airdrop has bounty, because when there is bounty, then I could say they have a bigger chance to profit, and with that bounty, ICO is also there. Most airdrops were just to gain more followers in their social medias and no ICO at all.Also,I think airdrop does not provide a great income for us, my advice is instead of you spending time looking for airdrop just start trading, because the income from trading is greater than following the airdrop (my personal experience) .