Football Outsiders rank special teams based on a variety of factors. (kick %, return yards, etc.)
They have Denver ranked 8th (unadjusted) and 10th when adjusted for weather and altitude.
The two missed FGs by Prater last week probably didn't help, but surprisingly, they moved up one slot - apparently as a result of yardage in the return game and other teams having their own issues as bad weather moves in.
Not surprisingly, Baltimore is ranked #1 and New England is #2. Strangely enough, the Texans are ranked dead last.
Edit: I was curious to see how this stacked up against their ST rankings for Denver in past years. It's the highest the Broncos have been ranked since 2002: