If I had to pick one: positional.
That said I don't see good reasons not to have both. Though it does seem that positional has a relative advantage for strongly typed languages and named for weakly typed. Java a method that takes a bean, a string, an int, then a boolean is a lot clearer than a ruby method that takes an object, a second object, another object, then finally an object.
So if you don't believe you have a cat, that's actually evidence that you have an infinite cat.