Paypal....although I don't have one myself, plenty of my friends do, and from what I've heard it's extremely convenient if your country supports it. But if I were you I'd accept to both, because some people just don't have access to it (and you can make more cash!).
I think paypal is generally the best but I think you should leave both open in case some kids don't have a credit card or bank account or don't wanna ask their parents to get a doujinshi or feel comfy explaining it. Or wanna pay themselves. But I think especially for overseas stuff Paypal is a safer and more efficent way to go.