I think for cryptocurrency, what is most important is do they stick to their white paper?

If they have 20% of their tokens devoted to 'other' they can do an airdrop. If it is 'marketing' that is a little less certain because a bounty or referral program would probably be better.

In the long run, if you are selling tokens, it is hard to argue you are not a security whatsoever since there is always doubt because you are selling 'something'. Open mining, bounties and airdrops get around that issue.

Airdrops are a little messy, however. Could you imagine a company having an IPO then having an airdrop for stocks? They would be kicked off the exchange that is listing them.