How to mask saved creditcard numbers in an app

Basically within our app users are able to save their preferred payment method.

I'm wondering if there is a best practice for displaying credit card info. So:

All numbers displayed: 234 1234 1234 1234
First part masked: **** **** **** 1234
Omit first numbers, mask 4, show last 4: **** 1234
Omit all masks, show last 4: 1234

Or any other alternative.