How do you find the right payment gateway for your eCommerce Store?

I think with stripe and paypal you can cover all your / and your customers needs.
I think you just continue searching if you have special needs that these platforms don't cover. E.g. we are based in the EU and had special privacy needs (GDPR) for a project, so we used mollie.com as an EU-based payment provider instead of stripe.
But stripe is definitely the more mature and more feature-rich platform.