You need to find a good altcoin first. I personally love Airdrop altcoins. After that, just hold them for months or years and you'll make a 100% profit at least.
Don't worry if it dumps a lot during this timeframe, it happens.
Remember that when you dump, someone is buying

I think the tokens that we can receive from airdrop are not worth much, just around $10 - $30. So even if we have 100%, it's also not worth much. I think the reward from bounty is better and of course earning token from bounty is also harder than airdrop
Yeah, that is true, comparing of the airdrops we have now and to the airdrops we had before, airdrops back then was a lot more profitable than the airdrops right now which are mostly shitcoins that ended up as a display in our wallet and has no value at all. In bounties, not all of the bounty campaign that you are going to join will give you the thing that they have promised after their ICO.
This days, ICOs are not that worth to be trusted at all, they are mostly will end up to be a scam and run off with all of the funds that they have raised with the help of all of their investors and bounty hunter who was left disappointed.