I think probably a lot of the time when people say others were the favourite, then their siblings would disagree.
Both my siblings can do a good "I was so badly treated growing up."
I can also say that they weren't. They tend to take individual situations, and often not actually think the whole situation through.
Eg #3 told us that he was treated badly because when we all went off to uni and needed things like pans, he didn't get the same. When #1 went grandparents on one side had just gone into a home so they got their things, when #2 went, grandparents on the other side were downsizing and so they got a lot of things.
You see he was really badly treated not being able to get those things from grandparents, wasn't he?
What he hasn't remembered was that instead dm asked him to look through the Argos catalogue and he got all the things brand new. And no, he's not sentimental and would have wanted hand me downs.
I suspect from things that have been said one of my siblings thinks they're hard done by, and I am the favourite, because they all live nearby but I don't, so when we go (about once a year) then dm tends to prioritise us for the week.
But she will drop anything for the rest of the year if they need anything, take them out a couple of times a month at least, go over if they're feeling ill, pay for things that need doing, and they often do things as a group all except me.
To me that's part of living near/further. But I suspect that sibling resents it.
We were treated differently, but mostly because we are different personalities and also situations were different. There was far more money when #3 was mid teens than when the other two of us were mid teens.
I don't think that any of us was treated better overall. We all had periods when things did go our way and we got more, and all had periods where things worked out less favourably.
My siblings always remember the less favourable times.