the fastest way to earn bitcoin and the safest is simply by buying the bitcoins and the most rewarding which should be considered the riskiest is GAMBLING with your bitcoins 
buying is not earning... But anyway, I really don't like the idea of gambling to make easy money... Sometimes the result is not in our favor, we release money instead of gaining when we are gambling, so I think it's a big "NO" to earning.
Gambling bitcoin is needed a skill and also don't forget with lucky as support.
It will feel so hard when you don't have both of these aspects. I think you must try another ways to earn bitcoin fastly and safety.
My advise is you should to try join on one of signatures campaign in this forum. At least if you high rank you will get 5-18 dollars in bitcoin every week. That number is decent worth if you ask me.
Its always better to earn it in a safer way instead of fastest way, and as you said signature campaign is really good to earn bitcoins and the returns are guaranteed.