Did the Samurai API have much weight in the decision making process? I understand if you can't share details here publically. I work for Litle and we are always interested in feedback we can use to improve our offerings.
The payments space gets confusing. There are gateway providers that serve merchants yet process payments through an underlying provider. At the end of the day there are multiple types of companies which can serve your needs.
I am bias since I work at Litle & Co. My team implemented the chargeback upload API years back, it's great to see it catching on.
Litle has some neat features including a JavaScript API for tokenization that we call Pay Page.
I won't go on self promoting, however I can answer questions if you have them. I follow hacker news because of my personal interest in software development.
