Till now I have got 10 airdrops. And polymath is by far the best airdrop I have received. It is one of the top 100 coins. Others does not have any value or have value less than 1$. If they are listed on some big exchanges, then there might be a chance of increase in value.

If you want aidrops of quality coins, then you must complete the KYC of some good ico's. If you are lucky, then they might decide to give airdrops. You do not need to participate in the ico if you don't want. Just complete the kyc. For ex- SelfKey recently gave some token to those who had completed their kyc.