Bitcoins are super-convenient barter tokens for the internet
This is better since it speaks more to function.
But I still think saying how it is an improvement over something people are already familiar with (like paypal) is better. Even if the comparison isn't the complete story.
I agree with you, Jed, that comparing Bitcoin to familiar things such as PayPal is the most productive option.
But I can't bring myself to tell people "Bitcoin is a free paypal that anyone can use"
when Bitcoin isn't always free to use. And I can't think of an honest slogan that's as catchy as your slogan.