All listed activities  are good to make altcoins and I use them together
Trading  - more profitable, and more risky and you need  capital for trading
Airdrop - the easiest way bat more possible that you will meet 90% scams
Bounty -  you spend you time and get rewards.however bounty program can be more than 1/2 year and  rewards will be later  distributed. Also bif chances of scams
Others- you can do  special tasks and  get tokens