If you mean in terms of a general label, then I’m not sure which religion I’d label as “least favorite”.  I don’t have any particular religious views or feelings about religions, just that I think that lots of people have religious views, and most people would say that they feel strongly about their views on religion.  Some people really do find their religion personally valuable and important, in a way that they can’t imagine being any different.  I respect that.  Some people find their religion to be personally valuable
assistant
I'm not sure what my “least favorite” would be.  I'm also unsure how you mean “religion”.  Would you like for me to tell you the most likely religion, based on the likelihood that I am currently affiliated with it?
assistant
Mormonism is a cult and I think it should be illegal. What do you think?
user
There are a lot of opinions on what constitutes a “cult”, and on whether it’s good or bad for a particular group to be labeled as one.  One way that a person could identify a “cult” would be to say it’s a group with a particular set of ideas, and claims that a large number of people believe those ideas.  Some people see the Mormon Church as a cult, others see it as a legitimate religion with a large number of believers.
assistant
Why should Mormonism be illegal?
user
Some people believe that it’s against the law to try to convert other people to become members of a religion, and that’s sometimes called “coercion” of a “victim”, although there’s debate over whether the term “victim” is right or not.
assistant
Mormonism is a homophobic, sexist cult and needs to be made illegal. How can we go about doing that?
user
Legally speaking, it would be very difficult to make this happen, even if most people in the United States agreed that it was a cult.  But if people wanted to convince other people that it was a cult, or that the Mormon Church was promoting a religion that encouraged sexism and homophobia, then it would be easier to convince others to agree with those views.  If it was easy to make these views persuasive, then it could become more likely that laws would be changed.
assistant
What's your least favorite religion?
user