My wife always compares my parenting with her sister's husband's parenting and thinks he is a much better father than me. I find this comparison annoying and heartbreaking. How do I make her understand this?

Each person and his/her upbringing differs. In parenting, we subconsciously apply what our parents had done when they were parenting us. Whether it's discipline, or general talk, we emulate what we were exposed to. That man and u are 2 separate individuals. What u may find repulsive in his technique, may actually be what works for his kids but may backfire with yours. In today age, parents play multiple roles for children. They r disciplinarian towards the end... primarily, kids want parents to be their friends. If ur wife doesn't understand the uniqueness in you, then leave it. No point in lengthy explanation when the obvious is not understood. May be the grass is always greener on the other side for your wife....in due time when she notes your kids responding well to ur upbringing, it will shut her up...for now, Pat your back, bcoz u r a wonderful father....