I have flown with civilian (PPL) and military instructors (UAS), and I have to say that I greatly prefered the military types. There is an element of consistency which I didn't find when I had to swap instructors during my PPL. Although I haven't flown with an ex military instructor during my PPL, I am sure that the standards that ensured they got the job done in the RAF apply once they leave the military.
The feeling I got from military instructors is the idea of always aiming to do things right, and not give it a go a few times, and if you don't get it, we'll move on.....
The only downside that I can see is getting clobbered by the QFI for being an idiot
(the BIG disadvantage of sitting next to your instructor in a Bulldog).
My tuppence worth
Cheers