I want to order the software with my credit card.

Is there any difference between PayPal or ShareIt?
Which one should I use?

There is no difference using PayPal or ShareIt when you pay with your credit card.

However, if you want to use some free email address to make the payment, you can only use PayPal. ShareIt! does not accept those free email address, e.g. @yahoo.com or @hotmail.com