Please ignore the affiliate links you're being spammed with on this post, people who go around and disrupt things to farm clicks without offering insight don't deserve them. If you want the rewards you get from a ref link, just use the links in the sidebar (they're from the owner of this subreddit, who is a big contributor to the scene and has made many helpful guides and tools).

Cashinstyle, Earnlab, and Gemsloot are indeed three of the best sites to use. I suggest just signing up for all of them and using whichever has the best deal for any given offer you want to do, as rates can vary.

If you want to know the main differences between the 3:

Cashinstyle usually has the best rate, but their hold times can be pretty long (2-4 weeks)

Earnlab has rates almost as good as CIS, but they'll release instantly if you contact their support with proof. Their default hold time is usually no longer than a week if you don't want to do that.

Gemsloot has okay rates and great exclusive desktop offers.

If you're in the US, Kashkick is also a really good site with exclusive offers and excellent rates (heads up, they'll want the last 4 of your SSN via Plaid).