Ask HN: which payment gateway do you use and why?

While signing up for a chargify account for my startup, we're kind of lost on what gateway to use.

Does anyone have experience with payment express? The setup fee is higher than the rest but the flat monthly fee looks like we would save money over paypal and auth.net. Also, payment express seems to be the only one who accepts currencies beyond USD and CAD.

So what do you guys use and how has it been so far?