The best worth of your time and effort is Bounty campaigns because it will offer you higher chance of getting good altcoins as most of the time more or less 4 weeks of bounty campaign and another around 30 days of waiting for the bounty stakes distribution and Hola! you can trade your rewards when they hit on coin exchanges.
Airdrops aren't that good to get because in my personal experiences, most of them are scams that's why this year I never joined any Airdrops but only signature and other bounty campaigns works better for me.