I worked briefly in sales at stripe, and most large enterprises are on or have considered Adyen. Keep in mind that many of these businesses will use more than one payment solution.
The business I’m working at now splits traffic between adyen, stripe, and others. Anecdotally, stripe has the best payment success rate of any of our providers.
Would love to learn more about that business -- I've pondered trying to build a payments API that could offer a way to transparently switch between payment providers, hadn't seen too many companies that were doing it
I know of Chargebee, Recurly, etc but I'm not sure those companies will let you actually spread payments between or if you pick one provider and use that. I've had people ask me if I knew of a company/product that could let them be less reliant on Stripe alone.
Interesting that Dropbox don't use Stripe? Seems a bit surprising as I thought YC companies generally use each others wares... I think the club aspect of YC is one of the most powerful to be honest.