I picked mine sort of like you did the first time... it just sounded about right. I remembered weighing 125 when I started high school and thinking I was huge, but I knew that was probably skewed by, well, being a teenager.
So I picked 120 (I'm 5'2") and went for it.
Turns out it wasn't a bad guess. I eventually got to 120, and knew I could lose 10 more pounds or so if I really wanted to
look my best, but I
felt pretty healthy at 120.
This time around I've done more strength training and have a bit more muscle, so I'm picking 115. Again I don't know if it's realistic, but I'll re-evaluate when I get closer.