Gambling is not an investment or a method to earn BTC imo since it's just random playing and can result in losses as well as profits and not like trading with an edge but the opposite with an edge against the player... Get paid to sites are profitable if you are in the US but faucets are rarely giving any decent profit.
Gambling is surely not an place to earn bitcoins but its a place to loose bitcoins and it is the most risky way to depend on earning bitcoins, if you are a safe player then best choice for you is signature campaign.
Well if you have extra money and just want to throw away then you should gamble. If you have high bankroll and afford bitcoins to lose then you can gamble. As earning bitcoin with higher bets easier then go from lower to high but the risk of losing a big amount of bitcoins is high too. But at the end it always depends on how much you can afford to lose. BTW its not the way to earn bitcoins.