The answer to your questions depends upon who you ask!
The auto-cpaps (any brand) are better because they also run in cpap mode as well as auto mode. You can use either. If you use cpap mode, you can use the auto mode for a "mini" sleep study once in awhile if you think something has changed. If you use auto mode, you can set a range of pressure that will allow the machine to adapt to you all night with a range of pressures instead of one set pressure all night.
The other feature that makes a machine "the best" is exhalation relief. On Respironics machines that's C-Flex, A-Flex or Bi- Flex. On Resmeds it's EPR. Actually I shouldn't comment, in detail, on other than Respironics machines because that's what I have and don't know much about the others.
The "best" cpap on the market are also "data capable" so that, with software and a reader, you can monitor your therapy each night or as often as you want and really know how your therapy is going.
Online at cpap.com is the most affordable place to purchase any cpap equipment.
If you ask me, I have Respironics Remstar Auto M Series with A-Flex and the software and reader to go with it, as you see in my profile, and I think it's great.