What's the difference between an airdrop and bounty program?
For an airdrop, you have to do an activity only once. After a while (mainly after the main sale) you will get your free tokens. Rewards are lower, due to lower effort.
For a bounty program, you are asked to do regular activities and you often have report all tasks which you have done to the project team to receive your tokens.
Bounty programs are worth more than airdrops, but the effort is not comparable. Please always keep in consideration, that some projects can fail. If that's the case you won't receive any tokens for the effort you've done.