With namespaced third-party libraries, do you use 'use' statements or call the class directly?

With namespaced third-party libraries, do you use 'use' statements or call
the class directly?

When using external namespaced libraries or classes, do you do in your code:
use /com/libwebsite/Package/Lib as Lib;
$stuff = Lib::getStuff();
or call directly?
$stuff = /com/libwebsite/Package/Lib::getStuff();
Thanks!