As the eldest child, with a sister only 21 months my junior, I was very conscious, even as a child, of all the privileges I got as the oldest child - bigger bedroom, often not sharing with two younger sisters and so on. As a result we decided to try and have two children, close in age who would be treated equally, regardless of sex or age, except where safety or law required it, and enerally we did pretty well, which was a good thing because, almost from day 1, DD(No 2) fiercely monitored all interactions involving her and her older brother. to make sure she did not miss out on anything and the playing field was always level.
We seem to have been successful because sister and brother get on really well. Their careers took them in opposite directions, and just cannot be compared, DH married and has children. DS decided against both having a partner and children, on the basis that she is far too uncompromising and demanding to sustain a relationship, still less adapt to bringing up children - and I think she is right. However she adores her niece and nephew, and they love her.
I would probably have tossed a coin to see who had the window first, otherwise, if the choice was not DD, I would be accused of favouritism.