Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
Firstly, psychologists and theologians alike tell us that folks are never really mature and adult until they learn to forgive their parents of any perceived mistakes in their parenting. So if you have grief with your folks, inevitably you're going to have to work through that.
In regards to your question, its not that parents love any of their children more or less, its just that kids are all unique and different individuals, and so parents have unique and individual relationships with each. Do you love any of your siblings or parents more than another? I'm not quite sure that is the case, however indeed you may like someone better than another, you may have a better affinity or rapport with different people, but love can be equal and the same. Love pushes us to do things we don't inherently like or want to do, and in our families we are always being pushed by this love.
In my own experience, my mother had noticeably different strategies with me to my younger siblings, indeed the oldest tends to have to learn responsibility to help out. Was my mother more lenient to them than me? Perhaps sometimes, and yet, I can vouch for getting in MUCH more trouble and my mom ALWAYS stood by my side, be it the principal's office or the court room. Whatever shortcomings I may have perceived, she always did her best to adjust to the individual person I was and am, and the differences between me and my siblings.
After all, keep in mind parents are people too, they don't start out perfect, they mature, grow, and evolve like the rest of us. Just as you are constantly going through physiological and emotional/psychological changes, so too are your parents. Simply put, they are not the same people they were yesterday, and tomorrow is an altogether different day. We have to be forgiving, we have to be flexible, we have to be loving.
We wear different mask and have different personalities in different situations and with different people. Parents are the same way. As we try to dissect our history and relationship with them, we have to always be aware that they are not perfect, and they don't pretend to be, because neither are we