I snored and was a mouth breather. My hospital test was done with nasal pillows, but I woke up a few times when I opened my mouth and air escaped out of my mouth (In through the nose, and out of the mouth).
I started on full face mask with the Resmed Quattro FX. This was the recommendation of the tech at the Dr's office. Seemed good for a few days, but it would ride up the bridge of the nose and develop leaks, usually blowing air into my eyes. I woke up with sore eyes more than once. I have an APap, so as a leak developed, the machine would compensate by increasing pressure, making this worse. I never slept more than 2 hours at a time with this.
Chatted with an Online DME, and they said many people complained about the Swift FX, and recommended the Resmed Mirage Quattro. I got this next, but it always leaked severly. Not around the eyes though due to the headpiece, but around the mouth area. Still never slept more than 2 hours at a time. Had wake up, reset machine, go back to sleep.
Finally paid out of pocket for nasal pillows, Resmed Swift FX nasal. It comes with small, medium, and large pillows. It has been a god send and I can finally sleep a full night, and wake up the machine at almost the same setting as when I went to bed. No leaks.
I do have the climate control heated line, and I did have to paly around with the temperature and humidity settings to find the perfect setting. No congestion anymore. Iritation where the mask contacts the skin can be solved with Lanolin Cream (Used to treat sore nipples when breastfeeding, available in any supermarket)
What I have learned from all this: You may need to try several setups until you find the right one. Don't blindly follow the "opinion" advice of your sleep tech. Some DME's are horrible to work with.
Good Luck.