It depends on where you are.
In the prairies, take a field because you don't have to deal with (as mentioned above) power lines (you might not see until it is too late), signs, cars, and the crown of the road taking you into the ditch.
If you are in the mountains or a heavily forested area, take the road, railway tracks or anywhere else you can get a clearing that isn't a swamp.
So, there is no perfect answer. It will depend upon location, situation and opportunity.