The real ones are those that don't require you to do any free online marketing for you to receive their worthless coins. Do some research online and you'll discover that the airdrop that have given the most profit are those that rewarded their early adopters or those using their platforms. We have the defi exchanges airdropping their governance tokens and others airdropping coins for holding a specific token etc.
I haven't heard of those that required you to tweets, retweet etc been much of a success and benefiting the participants. Coinmarketcap has some airdrop ongoing every weekday and the tasks are just too much then when the tokens gets distributed, you get just few dollars. This are the airdrop that are a waste of time.