Dropshipping is going to earn you more money, but it can be a pain in the ass, especially if the customers aren't satisfied with the product, or if you get a payment disputed etc, it will cost you quite a lot of time to run a dropshipping business but it can be worth it.
Affiliate marketing on the other side is probably not going to make you more money than dropshipping, but it's definitely going to make you more money than Adsense if Amazon has some good products related to your niche. Its also more easier to manage an affiliate store.
But the problem with social media traffic and Amazon is that you'll end up wasting a lot of traffic if some of your visitors are non-Americans, although this problem can be fixed by using a plugin like easyAzon, but withdrawing money from another country's Amazon such as Amazon.ca, or Amazon.de etc is going to be a problem. Even if you have tier 1 traffic from Canadian/Australian/English visitors, it will be wasted if you're with Amazon US affiliate program, but these people might convert if you have a dropshipping store.
So make sure you know your audience before you decide what you're going to do.