Proctologically Violated©® wrote:
Volume-wise, of course.
...

You really have to normalize for cost, too: volume per unit time per
unit cost. Otherwise, the biggest machine wins, whatever the type.

Given that, I'd say the abrasive cut off saw. I just tested mine: I cut
a 3/8 x 2" bar in 10 seconds. 1/8" kerf gives 3/32 cu-in or 9/16
cu-in/min. Cost is a lot harder, but the electricity component is easy:
15a x 120v x 10sec = 5wh (.005kWh) = $.00 +-. The 14" blade cost $6,
IIRC, and if it would do 100 of these cuts, the unit cost is $.06. The
saw is a better one (B&D Industrial) & cost $180. If it's good for 40
blades (??), 100 cuts per blade, that's 4000 cuts or $.045 per.
Operator cost at $20/hr (unskilled labor) = $.055. Total: $.16 per cut;
9/16 cu-in/min/$.16 = 3.5 cu-in/min/$.

Anybody want to do the numbers for drilling? Lathe, mill, shaper, ...?

Bob