No 1 is easy, Go for your main. As Billvon said, Conditioning will make the decision for you. It will also be a lot quicker.
I was once in a 4 way where we lost altitude awareness. We all got massive groundrush about the same time. All of us dumped our mains while still in formation. People on the ground say we were probably well under 500 ft when our canopys were open. Nobody was wearing a cyprus. Not one of us thought about the reserve. No time for that. :)