Ok, so if I want to do a payment or move some money - why should I use Ripple, when I already have Visa and PayPal, and perhaps also bitcoin?
The end user most likely won't be the one to choose this intially. Most likely you will end up using Ripple because a company is using the system and you'll have a custom app to access it.
Well, If I actually am the company, why do I use Ripple for my payments rather than the alternatives?