Ways to earn bitcoin:
1. trading. you must have special skills to get profit. you must know when the price up and when the price is down
2. join on bounty campaign such as social media campaign. you will get alt coin and you can sell it to get bitcoin
3. signature campaign but your rank must be jr. member or member to join the signature campaign
4. gambling
On the list that you made the best source of bitcoin is signature campaign. If you do trading but you lack skills and intuition then instead of earning you will lose your capital from wrong decision. If you do gambling as long as you are lucky then its good but good luck is always at the side of the gambling site and you will end up losing. That is why online jobs especially signature campaigns is the best source of bitcoin mentioned in your list.
From everything that he listed Signature Campaigns is one of the best ways to earn Bitcoin without shelling out your own cash/Bitcoin for you to earn. But signature campaigns are not an easy task to do, being part of a signature campaign you are representing a business or organization in which you need to also observe when you are posting, you need to post sensible answers or make sure you contribute to it, as they are paying you real money online, having low post quality is no option for them. Its like paying a person in full for a half work done.