I think a lot of parents still have favourites, and in many places, boys were (and sometimes still are) preferred. The idea was that sons would stay and take care of their parents, while daughters would marry and start new families. It’s not as common now, but it still happens in some cultures.
For parents today, I’m sure some still have favourites, but it probably depends on the family. Personally, I don’t think I would, but since I only have one child, I’ve never been in that situation.
When I was growing up, my brother was clearly the favourite. Me and my sister weren’t treated badly, just differently. Back then, it was normal for boys to get away with more and be given extra privileges.