Usually you earn tokens worth very little with airdrops (but you don't need to do actual work). Bounties it depends, I have earned very little sometimes (worthless) or I have been pleasingly surprised with more than USD 500 worth of tokens. I only do bounties for projects I like and invest myself, it is a way to earn more tokens you like on top of your investment, like the cream on top of the pie.
You are right, Tokens that you are going to earn is very little in air drops but the advantage is, It is free and i still prefer to join bounty campaigns because it has a huge amount of payouts when the sale is done so i prefer that you should work on promoting campaigns rather than waiting on air drops to come out.