My inclination is for more Rails-like usage and less typing. I personally wouldn’t want to have the helpers in their own namespace unless I needed them to be.
Perhaps the namespacing could be configureable? There isn’t a natural place for it just yet, but what do you think about the user having the option specify a namespace in an initializer? Something like this:
<pre>
js_named_routes :namespace => true # Routes.posts_path
</pre>
and/or:
<pre>
js_named_routes :namespace => "Rts" # Rts.posts_path
</pre>
And, by default helpers would still be in the global namespace. ;-)

I’m curious: did you actually run into a namespace conflict, or was this preemptive?