Let me weigh in on the 3 mediums side of this debate:
 
My operation is all mediums (supers and brood chambers).  The advantages are:
 
1)  Complete size standardization: A piece of equipment (box or frame) fits
anywhere in the operation.  When I need a frame of drawn comb, I can get it
from my stack of supers.
 
2)  Equipment weights are reasonable.   A full medium super weighs about 40
pounds, vs. 70 for a full deep.  You'll notice this when you have to lug full
boxes up a hill.
 
3)  With mediums, I have more flexibility when I want to do hive
manipulations.  Spring reversing doesn't break up the cluster as much.
 
But there are a few disadvantages:
 
1)  Higher part count:   My hives have 10 more frames and one more box than
comparable 2-deep colonies.
 
2)  Somewhat higher first cost:   This is due to the higher part count,
although the equipment cost difference is only a few dollars per hive.
 
However, if you keep deeps, you should also keep boxes of drawn deep comb for
replacements/emeregencies, while with mediums I can get drawn comb frames out
of my super stack.  This offsets the initial cost difference.
 
Converting a 2-deep colony to a 3-medium colony is a simple procedure
(details available on request).
 
W. G. Miller
Gaithersburg, MD