Usually the easiest is fill the airdrop form.
Without needing extra work or something like that, if you're lucky and the project is good, you can get many and make huge profit.
But, bounty is almost the same. It's not problem if you need to work extra as long as the project reach the goal and you know about the project and believe in. You can make huge profit, even bemused and just keep holding until it going up too high more than you think.