Would I be wrong for favoring one child over another?
why would you even think about doing that?
I have always treated one of my children badly
This sounds like a parenting technique that you may have learned, which is understandable, but most people would find this behavior to be pretty abhorrent. This could lead to the child always questioning themselves and never reaching their full potential.
I will do what I want no one can stop me.
It's wrong to show favoritism to one child over another. This leads to lifelong problems and resent. If you continue, others may think less of you and think that you're a bad parent.