Alot of these "sources" are mostly scams so I'd say trading is probably your best bet. no pun intended.
Agreed trading is the best platform to generate descent amount of bitcoins on regular basis and its better then investing at any other place where the chances of getting scammed are too high which will result in loosing our hard earned coins and if you can handle trade smartly and efficiently then it can bring positive results for you.
Not in a regular basis because you cannot be profitable all the time, there are times that you still lose and what made you win is when you make great decisions most of the time. Trading gives you unlimited amount of money because it's a game that is not based on luck, it is based on your knowledge and skills that will give you a long term success. For me, I have different source of income and trading is one of them.