I think I posted this before, but I have the same mask that lowviz is using for testing - a Mako Minimus. For me, it has been my MFH. I tried toothpaste and burning, repeatedly, and it still wanted to fog.
After reading earlier parts of this thread, I ran it through the dishwasher, using a pod of Cascade Platinum detergent. Since then, it has been mostly fog-free (using diluted baby shampoo on it before each dive). I say mostly because sometimes it leaks. When it leaks, exhaling through my nose usually ends up causing it to fog after a few times of clearing it during one dive. I would say it is still a *little* more fog-prone than my other masks in the same circumstances. But, in practical terms, it is now fine for me.