I'm dealing with mites right now, and will be using Sevin. I actually wanted to use Eprinex, a cattle dewormer, but I don't want to shell out almost $40 for more dewormer than I really need.
Mites will become a really bad problem if left untreated, so I want to kill them dead the first time! I will clean out the coop and pressure wash it, then spray it with liquid Sevin, then dust all the birds with Sevin as well. Most people say to just wash the eggs (which I have to do anyways if I sell them.). Sevin is actually one of the less harmful stuff out there.
I don't have time to try DE, because I can't be doing an ongoing battle, though I will say I used DE on my goat when she had lice and it worked well.