I would think a lot depends on the demographics of your market. Impulse buyers will be deterred by a non-standard payment method, meaning you have to have the most common. An audience like ycombinator readers will be more likely to evaluate, sign up, and use something alternative, and may be more likely to refuse to use Paypal at all.

My advice is to pick on what is easiest to integrate with at first. Regardless of the payment method, you should be able to validate the idea by getting at least a few customers, and then add payment options going forward.