@mike-i Having used both now, I lean more toward OpenPhone myself, mainly because of the better price and interface, as you said.
I actually remember having more of these issues with RingCentral. Not so much with jitteriness, but it felt like there was an annoying 1-2 second delay on some calls.
I’m not an expert, but I think most of these services are built on the same technology. The big differentiators you’ll see between them are the price, the user interface (which is a big deal… because some of them are not good at all), and the quality and responsiveness of customer service.
If anyone else has better expertise on what differences exist between them, feel free to chime in!