If you are looking for a way of earning which will give you a highest profit within shorter time then trading is best option for you. If you are looking for an easiest way but with low profit then bounty is the option for you and airdrop is also good but it give too much lower amount which cannot help you in your living. ICO investment is also better and best point in ICO investment is that if everything is legit in ICO and they complete their project then the profit from their coin is confirmed.