Hello, @alessio_v85,
I think there is no best way to use one or another JS framework with
rails. There are some best practices but I think you should pick one
that fits to you.
If you need an example of Rails Api with separate ember app check out
"Sean Devine"s Live Code a Charity Auction Application: Episode 1 on
youtube.
I found it to be a great example but a little time consuming to the
through all this episodes.