If you aren't looking to gain a particular coin/token mainly then airdrops/bounties can net you a low to sizable amount of altcoins with a wide range value. Obviously this a very unstable source in order to gain altcoins, but it a "free" source nonetheless. Trading tokens already in your possession for altcoins is clearly the easiest way to earn them/ seeing the value change over time. Of course with the aforementioned method you aren't necessarily risk free like you are doing airdrops/bounties. With the current bearish market prices are very reasonable if one wanted to invest fiat.