Up side to all mediums:
Everything is standard. One size box, one size frame. If you have a honey bound brood chamber, just swap a partially drawn comb from a super with a frame of honey. Supers are too heavy to lift very high when they are deeps.
Downside to all mediums:
More frames to look through to find a queen. I think the queen lays a little better pattern in a deep frame.
I'm standardizing on all mediums, partly because of PermaComb and because it's only available in mediums.
I was standardizing on all deeps, but the supers were killing me.