I'm building an application that requires Facebook authentication and Paypal Express payment. Looking around has led me to the following gems:

https://github.com/nov/paypal-express
https://github.com/plataformatec/devise
https://github.com/intridea/omniauth-oauth2
https://github.com/mkdynamic/omniauth-facebook

I'm not familiar with gems that would be best suited for this goal. So are these some of the top picks within the Ruby ecosystem when dealing with Paypal Express Payment and Facebook authentication integration? If not please suggest alternatives for me to look into.

These are questions I'm asking myself:
1.) Goto standard for solving problem within Ruby ecosystem (collaboration over competition)?
2.) Are these gems well maintained?
3.) Battle tested?
4.) API well documented?
5.) Well written?

* Mostly I need help with 1.) because I'm rather new to the whole Ruby ecosystem.

Thanks