[hinkley]

I run into a similar problem trying to chose libraries for projects.

There's one project that is 'active'. Are they active because they're better, or because they arrived late to the party and are reinventing the wheel.

This other project is 8 years old and has hardly been touched in 2 years. Is that because it takes 4 years to cover the entire domain and a couple years to fix all the bugs that can be fixed? Or because it's languishing?

Novelty is not a good selection criterion. Sometimes the old ways are best.

[stanislavb]

You can have a look on LibHunt next time. Apart from project activity, you can compare different libs by their relevant popularity. That should help you make a better decision. E.g. https://ruby.libhunt.com/categories/21-a-b-testing

(disclosure - I've built libhunt)