Google Checkout then Amazon payments for me, but either would be fine.
Like a lot of people I'm vaguely uncomfortable with giving credit card details to companies I haven't heard of before & whilst I have a Paypal ID, I only use it for those places insist on Paypal (eBay mainly), so I can never remember the password and have to look it up. (Yeah, yeah, KeePass et al, I know, I'll get round to it at some point...) I use Amazon and Google often enough that logging in to them in order to make a payment isn't such a hurdle.
Like a lot of people I'm vaguely uncomfortable with giving credit card details to companies I haven't heard of before & whilst I have a Paypal ID, I only use it for those places insist on Paypal (eBay mainly), so I can never remember the password and have to look it up. (Yeah, yeah, KeePass et al, I know, I'll get round to it at some point...) I use Amazon and Google often enough that logging in to them in order to make a payment isn't such a hurdle.