I've been looking around for an entity architecture for a while now. I've used a traditional inheritance model and experimented with a self written mixin system. For my next private project I wanted to experiment with entity component systems. I found a lot of great articles about it and I generally like the idea behind it. I don't want to create my own implementation right away but use an existing, proven one. I found entityx & anax. Generally I like the style of entityx more and the integrated event system is a plus, too. But then I found this article showing entityx has quite bad performance in comparison. Also anax seems to have a more active github repo. I know this is an opinion based question but I would appreciate some of your thoughts on these libraries since information about them is quite sparse.

Performance is always relative. The article you cite says that EntityX "provides the least verbose API and the most functionality" and that is usually what matters.

It's also worth considering that microbenchmarks like the one used here may not be an accurate reflection of real-world performance. It might be the case that EntityX scales better to multiple component and system types than the other choices do. It is also usually the case that you don't want to be calling update() on every single thing every single frame anyway, if performance is truly an issue.