There is no simple answer to this question, and it depends on many factors. Beauty blogging is a very broad topic. The best beauty products to sell online are those that complement your content. If your blog posts are aimed at professional makeup artists, then you will want to promote professional makeup brands.
On the other hand, if your posts are aimed at an audience of teens and young adults, you will want to focus on brands and products that will appeal to them. For example, if your audience is of a younger demographic, you won’t get any sales if you are promoting anti-ageing products intended for a middle-aged demographic.
The bottom line with affiliate marketing is you have to keep testing, and trying new approaches, different offers, and promotions. Based on the results of these campaigns, you can then identify the best beauty products to sell online.