OK - I don't know much on the Respironics lineup. I occasionally see one pop up at what may be a deal price, but I don't know enough to know what I am looking at as I find their naming/numbering conventions confusing.
For Resmed, I get the whole "avoid the Escape" models if you want data. What would the current Respironics analog to the Resmed S9 AutoSet or the "AirSense" 10 AutoSet ("AirSense" makes no sense to me - why it is not just the S10 - why say things in eight letters that can just as well be said with one?)
Auto, heated humidifier, maybe climate line tube (assume you can substitute normal slim line tube), data dumping (assume sd card)?
The PR System One Series 60 auto aflex with heated tube humidifier "the model 560" would be the PR machine that is the equivalent of the S9 autoset.
The Pr system one model 550 is basically the same machine but with a slightly different response time and no heated tube.