When I was in paramedic school over 10 years ago, I developed a preference for the Miller for one reason...
We started intubating plastic manikins before peope, and the less pliable manikin had that plastic epiglottis that always got in the way.
With the Mac, even w/ proper technique, it still didn't move right, so I got used to having the Miller to move it out of the way.
Then, it just became the familiar choice.
When I started my anesthesia rotations, my preceptors made me try the Mac, and I have to say, with a much more "pliable" person, the Mac worked just fine.
I had a guy w/ post radiation fibrosis in the neck, and when I tried a Mac it felt like the old manikins. I ended up using a Miller to get it, but in retrospect, can't you just use the Mac to pick up the epiglottis? Not the way it was designed, but it seems like it would work just fine.
(Also, I've started to like the Mac for having the flange to help push the tongue aside. )