Using Sleepyhead to understand and take charge may prove to be more important than the machine, as long as the machine is a current-generation ResMed or PRS, and fully data-capable, and comfortable for you and your sleeping environment.
As you know, mask fit is frequently a bigger issue than the choice between those two modern machines. Getting a mask to fit _you_ comfortably without significant leakage (so it doesn't keep you from falling or staying asleep) may be the more important consideration.
I have only good things to say about the ResMed Quattro Mirage - but it still doesn't fit my peculiar face perfectly. Everyone's face is different. I think that the Quattro Mirage manages to adjust to fit more faces, which is a very good thing in the sleep lab, and it's been the first mask to work for me in the long term - but YMMV.
Good luck and be persistent, especially with the DME! There's a wealth of useful information and advice to be found on this board!