I believe that everyone who is not an only child has, at one time or another, said/thought "{brother/sister's name} is Mom's favorite." It is an inevitable part of growing up. And in my case, when it seems as if the sibling has received far more from the parents/Mom than you have, the proof is right in front of you. I am one of two children and I am the mother of two, so I have seen this issue from both sides.
Whether it is true or not, I feel as if The Brother was always the favored one. He DID have privileges I never did, simply because of his gender. Also, because he could never sever the apron-string ties, he has gotten more materially from The Parents than I ever did. While I *think* I have gotten over most of the 'slights' I believe I suffered, it is kind of hard to go through life feeling as if you were not the favored child. But life goes on.
I have tried my darndest to be as even-handed with my girls as possible. I know I haven't succeeded as well as I would have wanted to, but I have tried. These days it is difficult to give equally--materialistically, that is--because of where each lives. The Youngest lives 8+ hours away and The Oldest is only 2 hours away. Also, with The Youngest not having any children, we give much more to The Oldest and the grandchildren. Yet, we do the best we can.
The Oldest has ALWAYS been the one who cries "You love A better than me!!!!! She has ALWAYS been your favorite!!!" I can't say that A doesn't feel as if SHE isn't the favored one--and she probably DOES feel as if we 'love' her sister best--simply because she is quite closed-mouthed about most things. This is just part of growing up with siblings--kind of like "Tell him/her to stop touching me!" :)
The Oldest can't believe that I actually did this, but I have attempted to analyze whether or not I have a favorite child. Over the course of several days, I thought about each of my girls and what I felt. I looked at their good and bad sides and tried to determine if one had the 'edge' over the other in my affections. And my conclusion was: I do NOT have a favorite daughter. I love them equally, but in/for different ways.
The Youngest is possibly the sweetest person to ever live on this earth. She is kind and helpful in ways that put me to shame. She is The Animal Whisperer--her connection with animals is the most amazing thing I have ever seen. She isn't a complainer--actually, she keeps things to herself that she SHOULDN'T. Soft-spoken, always with a smile, and with the greatest dimples ever to be seen on earth. Kind-hearted is much too tame of a description for her. She has become a world-class baker and enjoys doing it--and this has freed me from having to do the baking that I did for so long. I love spending time with her and we get along very well--she was my rock, my friend, when we had so much trouble with her sister. (She DID give us trouble, also, but right now I'm just going with the positives. ;))
The Oldest is the most amazing woman on earth. She manages--I have NO idea HOW--to keep a household of 9 people running rather smoothly. She loves her life and wouldn't change anything about it--other than have more money, but which of us DOESN'T want that ? ;) My Oldest could/would/and does talk to doorknobs, and can get a response! Social situations have never appeared to frighten her--her confidence around people is something that I envy more than I can say. She will MAKE time if someone needs her help. She is bold, opinionated, and she doesn't care what others think of her. In many ways, she is who I want to be when I grow up. :)
If I needed to pick a favorite of my two girls, I would have to admit it is not possible. Each is amazing and the only thing I could possibly want more is to have one person that combines the best of each of them. But then I wouldn't have the pleasure of loving TWO such awesome women.