I have to agree with Evo here. Sheer enthusiasm and wanting to do the job makes a world of difference, regardless of the level of experience (although the more experience the better I hasten to add).
I've been fortunate enough to have flown with both, having done my time in the UAS system like Boing_737, and recently completed my CPL/IR.
My primary QFI in the UAS had no enthusiasm for the job at all, and it showed in his instruction. I learnt so much more when I flew with the boss or any of the other QFI's. They absolutely loved the job and it showed through. The boss was a fearsome old b#gger and his standards were way higher than my primary's, and eventually it showed through in my own flying. I think the military environment allows FI's to be a great deal harsher and more demanding than many civvy instructors would get away with, as there are no commercial considerations.
When I did my CPL, the quality of instruction was OK (it was easy to make comparisons as we were covering a lot of the ground I had done in the UAS), and some of it was good. The best were the old boys who had been instructing for many years and had a whole load of experience to pass on, as well as enough enthusiasm to have kept them in the job. Some of them were every bit as much fun to fly with as the military guys, but they are obviously teaching with a different end result in mind.
I suppose the final answer would be it depends what it is you are looking for personally from your training.