Best source of bitcoin used to be signature campaigns here, but the payout these days is very less as compared to old days.
Now the best source of bitcoin is trading and investing them or maybe giving a collateral loan to someone.
I agree with that, signature campaign is really one of mg favorite way to earn bitcoin, next to trading. Though I do not really like making some collateral loan because sometimes they make a run from the one who made the deal or the one gave the loan, but that is really rare because we are using escrows to witness the loan. I did invest my money on bitcoin, but I dont think I can invest on something like gambling sites, trading is a good choice too but we must learn a lot of things before taking on trading because trading, also has a lot of risks.
There is no doubt that signature campaign is the best source to earn bitcoins nowadays but the payouts are limited so it will not give you the best results that you are looking for and you cannot depend on those earnings for living and if you want to earn satisfactory amount of bitcoins then that can be done only with trading.