Best experience from an airdrop was Polymath, think it'll be a hard one to beat. Got 200 free tokens at an opening value of around $1, pretty much sold those straight away. Have had a few worth $30-40, and lots between $5-10. Still holding some really low value ones in the hope that one hits the big time. Most were from 4-6 months ago, haven't really done many since as the general value of most seems to have dropped, but check out options now and again to see if there's any worth doing. Just a lot more selective now.