I don't have 3 but 2 of opposite gender who share, and I would let them decide, but my preference would be your Option 3, with initially the oldest having own room. All depends on the children, but my DS frequently wakes up DD too early e.g. 5:30 - and this year at kinder she seems to need more sleep than him, and from what I have heard when they start school they are even more tired - so based on that, I would choose option 3, but I think the ideal combination will vary over time.

I am working on needing to have boy/girl having their own room by time the oldest gets to be about 8/9 - although I don't really think is that big a deal if have to share after that (when I was 16/17 I had my brothers room for a year and my brother and sister shared (14 and 12) for the year to help me with studying for final exams)