Well after all the post here still gambling is still the fastest way to earn bitcoin . But dont be amazed to the "fastest" way. It is the fastest way also to lose all your btc.
You can't earn by gambling, you can only win by chance, which is smaller than to lose them. Gambling should not be considered as a method to grow your bitcoins, but to spend spare bitcoins for entertainment of playing in casino etc..
You can earn in gambling
Just dont play those slots , dices, casinos etc in gambling sites. Much better to place your bet in sports betting. No system , all is fair. But of course afterall it's not a method. I just said it is the fastest way to earn btc.