At least with airdrops you don't invest your time in promoting the project, translating the whitepaper etc, you just receive the tokens or don't
bounty and airdrop can turn out to be worse, it's a sad fact. that's why we have to analyze the value of the coins/tokens before we join the airdrop or bounty. REBL is one of the good coins that turns out to be very valuable (atm at least), and they distributed the tokens by airdrop (but somehow it looks like a mini-bounty to me).