I disagree, the worst is Rasika by far. Any mother who stands by and happily watches her son beat his wife that too in front of a child is a horrible parent/mother in law. Vandu has been through hell with Ajit and Rasika
Savita, she hasn't always been the best and there was a time she was the mother in law from hell for Archana. Archana really went through a hard time but fortunately Savita has changed her ways and is really good to Archana now, she loves her like a daughter and has seen that Archana is not a bad person at all
Bhavna, she has her flaws and there were times she was bad to Varsha but overall I think Varsha has been the most fortunate to get a mother in law like Bhavna. She is a good person and treats Varsha well
Sulochana, I'd vote her to be the second worst after Rasika because I hate what she is doing to Archana and Manav. She is repeatedly taking advantage of their goodness and it is time that stop. Sulochana needs to take care of her own problems and stop burdening Archana and Manav, Vaishali and Varsha don't need anyone to take care of them they can take care of themselves. It would've been better had she told Archana to take care of your sons, they need you.