(Ofc, another caveat is how accurate do they monitor and report, but---short of running customer sentiment analysis---I don't seem to have a choice other than to assume that factor is roughly equal.)
I guess it's a David-to-Goliath comparison but I would just expect Cloudflare to have better reliability than any of them. Plus, as another reply pointed out, brand recognition helps in getting that budget approval.
The reliability isn't great though. "Elevated Rendering Errors" almost always is "increased errors rendering uncached derivative images". Basically any image variant - by file and transformation/dimension parameters - that hasn't been viewed recently won't load. So a srcset homepage hero image probably has all size variations a user might see in Imgix's cache, and will render. But on less-traveled parts of our site, photos generally won't load. We're a rather image-heavy site and it's pretty debilitating to the UX when this happens, so it's frustrating that this happens more than the "almost never" rate we'd wish for. FWIW, we've never noticed problems on their end that aren't closely followed by an incident report in their status page, so they're not under-reporting at least.
In general though, CF just nail every version of what they do so I'd personally go with their version of it even if it's the same.
Is being a cloudflare fanboi a thing yet?
This can be handled by a CMS. E.g. Media Cloud, a WordPress plugin that integrates with IMGIX.
Coming from an enterprise getting approval to use a new SaaS vendor is painful.
But if a existing vendor has new product offering, you skip a lot of painful TPS style application forms.