foxmoth:
Most instructors will pick a field for the demo and probably help pick the first one or two fields, after that it should really be down to the student - I know of very few
examiners that will pick the field for a candidate!
I know one or two... when I did my skills test it was picked for me... tbh I found it harder. I was positioned downwind from the field, the examiner pulled back the throttle and said, "Your engine has failed, thats your field there (and pointed) land in it!" Then he just sat back and watched me try and sort it out. As I said before it was pretty windy, 25ktG35kt... which made things good fun when I had descended below 1000ft.
Think it would make an interesting topic, I myself feel either way would be fine, I think you'd get a pretty good idea of the student's skill level by picking the field for them, ie their ability to judge the wind and ability to position the aeroplane adequately to make a successful PFL.