Where are you located? I ask because Milgard is no longer available except out West, and Plygem has different offerings depending on region. I would not consider the other choices personally.
To answer your question:
1. They should all be relatively close in "ease of use", so I would not give that much weight in your decision.
2. Certainly fire escape is a valid concern, however given the fact that I have children of the same age range, I'm not sure that I want them to know how to open and climb out those windows on their own. I have to think the odds of them climbing out the window and getting hurt on any given day would be much higher than that of an emergency situation arising, coupled with a 5 yr old remembering and acting on a planned escape route. As a matter of fact, most people that I meet with young children love night ventilation latches primarily because the kids can't figure out how to open the window far enough to fall out ... Just a little bit of personal commentary there, please take no offense.