Here are some blog posts that are useful for finding good bitcoin affiliate programs...

https://99bitcoins.com/get-earn-bitcoins-massive-list-of-bitcoin-affiliate-programs/
http://www.gr1innovations.com/bitcoin-affiliate-programs.html
https://makeawebsitehub.com/best-bitcoin-affiliate-programs/

What I did was sign up for the ones that they all 3 mentioned because I assume those are the best since it was coming from multiple sources.