In reference to the question at hand, I believe the DIR answer is we choose our tanks based on a risk/benefit analsys. Assuming one knows how to dive doubles correctly (and has a balanced rig yadda yadda) the doubles will never hurt you unless there is something like a difficult climb to the dive access point or difficult entry/exit.
My choice usually is made by:
Shore dive shallower than 60' and not in icing season: single
Boat dive, icing season, deeper than 60', wicked easy entry, rather low vis, or for a training dive: doubles
I'll dive a single in warm water down to about 110', but only if conditions are good and the team is on the same page for the rather high rock bottom for this dive.