Sanam and only Sanam. She was smart, independent, courageous, feisty when needed and always had a positive outlook on life.
Did she tone down her "feistiness" when she came to Bhopal? Yes!
The way I saw it, the girl went through a lot not just with everything that happened in Punjab but she had many downs when she reached Bhopal. Not only did she almost lost her life but she almost lost her badi ammi... the person closest to her, the person who raised her, her world. I didn't think she turned into a doormat (at least not at that point), she matured and was learning from life experiences.
Life is not about yelling at top of your lungs to make a point, it's not about getting even. Life is meant to be lived and enjoyed and to a be a decent human being. Doing good without expecting anything in return. That was Sanam and I loved her for that.
Her character was butchered later on to accommodate the twin track. I never understood why Gul & Co thought they couldn't just have both sisters be smart and courageous. All the sudden Sanam couldn't stand up for herself, couldn't fight her own battles and she needed her twin to do everything for her.
No comment on Jannat, other than having nice clothes, she was a complete dud!
I never watched Season 1,so I only know Zoya from flashbacks. Which is obviously not enough for me to comment. Nor am I watching currently, so I don't know about Mahira but from the comments and posts in this forum, it seems she is the worse character that SJ took on.
These are my personal views/ opinion.