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.
That's true. Also, I think many prefer bounty, because with it, at least you have the chance and capability to control what you can probably earn. Unlike in airdrops where you have to wait and see how much would you get. Plus, airdrops are just company schemes to saturate the market with their coins, so generally, they won't give out a lot to one person because they want the quantity of having more people hold their coins or tokens. Also, there has been many bad happenings with airdrops being used by companies or people to steal information and get other people's holdings.