Most effective Bounties have been and is still conducting on CH Bounty. I have participated in 3 Bounties so far and have got all my tokens, currently you can check
Unitlanat's and
TYDO's bounty campaigns.
I think that Bounties are quite better than Airdrops. Airdrops nowadays are almost worth nothing so it would be a waste. Bounties may take some time to be finished but the reward is worth it, and is much better than Airdops.