In Maryland, by far most people use 2 deep brood chambers, with 3 medium
brood chambers also common. I don't know of any Marylanders who use single
deeps for anything but new colonies (and comb honey production).
In our club's short course, we advocate using 2 deeps or 3 mediums as the
brood chambers.
Personally, I use 3 mediums as the brood chambers.
W. G. Miller
Gaithersburg, MD