What is the most appropriate ladder to use to cut a 14ft hedge
I would say a couple of those 'A' frame type things (sorry, don't know what they are called), with a hefty board between the two. Or a very sturdy step ladder with a decent platform to stand on.
How many times a year do you need to do it, how long is the hedge, and what is the ground like? Any ladder would need to be at least 3 ft taller than the hedge when positioned at a suitable angle.