Will only give a brief description as I'm not sure if people involved are on here :)
We have one DC and another on the way. Finally got around to sorting wills recently and we have to decide who we would want to be their legal guardian. I was under the impression we would have my sibling (not in a relationship but we see them daily and they live where we live) and OH was under the impression that his sibling would be the more likely choice (married with children of their own, nice enough but live far away and move around a lot. We see them 3 or 4 times a year)
I'm unwilling to uproot our children if the worst happens and send them away from what is familiar to them when my family are here. OH is unwilling to believe that anything other than a married couple would be the best choice. We are not married FWIW!!