Currently Stripe works best if you can use it, you should use it to process your purchase of XPadOne.
There is a slight issue that may impact purchases through PayPal, it may get you stuck in a loop where it says 'Something Went Wrong' and then display a button to go back to merchant.
If this happens and you have the option to, you should use the Stripe processor.
Stripe is used by many merchants as it is a common secure credit/debit card processor.