I have worked as an engineer is private and public power utilities and there is not a significant difference in how efficiently things get done. All human orgs are basically the same, when you get down to the people actually doing the work. Private utilities have all the security of a public utility so the 'profit margin' is not really an everyday focus at the worker bees level in the way that it is in actual private industry.

Having seen the sausage being made in both, I would say that private utilities are very little for the additional $$$ they extra t for shareholders. I would just as soon see all power production and transmission nationalized.