Apple was the only one whose policies explicitly limited the info it gathered and shared from users and their payments. It didn't store card numbers, and it promised not to sell data. It also asks you to confirm every payment, so you won't send money to someone by mistake. To no one's surprise, its limited platform support was the main setback in the test. You not only require an Apple device, it has to be a reasonably recent Apple device.
Not that most of the others spelled trouble. Venmo, Square Cash and Facebook Messenger were all considered slightly above average in most respects outside of privacy. The bank-backed service Zelle was the main straggler. In addition to unclear data policies, it didn't include a way to confirm payments in its main mobile app. The service promised to add the feature by late October.
As you might have noticed, this wasn't the most comprehensive test. CR didn't include absolutely every service, and was quick to acknowledge that it hadn't put Google Pay's newly integrated money-sending feature through the ringer. Look at this more as a survey of popular options, not to mention a list of criteria to look for if you're still on the fence.