What is a difference between adsense and affiliate marketing
Affiliate Marketing is the performance driver marketing, where a business rewards the other in terms of transferring traffic or conversion. Adsense is also a kind of affiliate marketing only, but it is a Google product. When you have a blog or website, you wanted to allow your website space/inventory to Google to run ads there you will register on Google Adsense, once approved Google will start running ads there and depending on the quality traffic goes away from your website after clicking on the ads you would be paid by Google.
If you are thinking to create an affiliate vs adsense strategy for your blog or website, I would recommend to try out both, look for the best affiliate as per your website content, they usually work on CPC or CPA models.
I hope this will help.
In addition to what Deepesh said, one more thing that makes Adsense a better option is that with lots of advertisers vying for spot, your inventory will always be full i.e. there will always be some kinds of ads available for your webpages. That translates into steady income.