I suppose the answer would be different for different people.
But in my case I wanted to attend a church where the gospel of Jesus Christ was preached, where there was fellowship among the members of the Congregation in the Holy Spirit, and where Jesus Christ was worshiped enthusiastically.
My experience being raised as a Catholic was of an emphasis on the outward conformity of religion. No Catholics of my acquaintance, either family or friend, ever read the Bible, spoke of the importance of Jesus Christ to them, spoke of what the Holy Spirit was doing in their lives, or ever witnessed to anyone on the importance of being saved.
So feeling that these things were indicators of an unhealthy (or dead) faith, I decided to seek out people that had an open and enthusiastic Christian testimony. Maybe it’s just a function of where I live, but the ‘Fundamentalists’ outstrip the Catholics in the enthusiasm department.
My experience with the Catholic church was of dead, repetitious, ritual. No fire, no desire, no fellowship, no Bible study, no evidence of the Holy Spirit at work. The only time there was ever anyone new in the congregation was when a new family moved into town. But at least the Mass never went more than 45 minutes.
Peace