Best source for bitcoins are trading and buying a good coin under ICO. My second choice is signature campaign.
As far as I am concerned hyip, refshare, mlm, cloud mining, other pyramid schemes and gambling can't be considered as a source of bitcoins, as you will probably lose them.
There are also more ways to earn bitcoins which are not mentioned in poll, for example lending, investing in gambling site bankroll, selling something etc.
Well buddy there is confusion with your answer I guess you are confuse by yourself to what to say referring to your answer in the same you are saying that you dont considered the gambling as a source of bitcoin because you can lose it and at the same time you are saying to invest into the gambling site. It really dont makes a sense, am I right?
But I like that ICO trading idea. This is really cool when you get offers at a cut price rates and then sale it on the regular price.