It is depend on which airdrop coin you got ? If the airdrop is shitcoin sell it while you can or you will never possibly can sell it. But the airdrop is like bitsend airdrop or deep union last year you need to hold it untill year 2021 so you can sell it with very good price. For your information : ripple and stellar was an airdrop coin when it is first launch in 2014 and now both coin worth billion in marketcap. Not all airdrop tokens gotten are traded immediately. Some do not list early and even after listing sometimes, the price might be ridiculous. Also, before dumping any airdrop token immediately after listing, try to study the project first. There are some airdrop tokens that worth holding.