E-commerce with Google Checkout or PayPal Website Payments Pro

Which one would you recommend? Google Checkout or PayPal Website Payments Pro

Have you had any experience that might shed some light into the subject? A client has just accepted my proposal to create his e-commerce site.

Now, I have never worked with neither Google Checkout or Payments Pro, I know, I know, I shouldn’t have presented a proposal without knowing how much work was involved. But I did it because it’s going to serve me as training too, I mean, how hard can it be, right?