Nowadays many ICOs offer free coins, but we have two problems with this free coins, the first one the value of this coins will drop after start trading due to a lot have free coins willing to sell it, and the second they ask for your ID (KYC), and i think it is very risky to send your IDs to any one.Please vote to help others
If you prefer to working easy without much efforts, airdrop is the most suitable for you.
Another cryptocurrency activities such as trading, bounty hunting, or investing will consume your power and time.
But the profit you can generate in airdrop will be much lower than other activities.