The single most expensive resource in development is the developer. I could write everything in optimized assembly, using minimal machine resources to either write my software or run it. Of course that would mean I have to run my desk lamp for like 100 hours instead of the 1 hour it would take to write it in Lisp or Python. And don't forget the megajoules of food my brain would burn.
I really have no idea what would be most effective energy-wise overall, in the end. It's a curious question.