I don't use Stripe but my understanding is that it has dominance in its space. What are the competitors? BrainTree? Google Pay? Why haven't those services eaten Stripes lunch?
+ there are a lot of local players, e.g. Mollie is popular in the Netherlands, Payu and Przelewy24 are large providers in Poland, in China people pay with Wechat and Alipay, and in Indonesia with GoPay by Gojek
Stripe provides a lot of services besides payments, but if you just need a payment provide for your on-line shop, whether you go with Stripe or Braintree is not a very big difference. I mean sure, quality of documentation and customer service matters, but the 2 most important factors for people are pricing and support for the payment methods popular in your country (e.g. iDeal in the Netherlands, fast bank transfers in Poland etc.)