At least when I was growing up it was the New International Version. You were a fundie if you insisted on the KJV or the NKJV among people I knew.
The NIV changed their interpretive philosophy around the turn of the century to favor gender neutral language. Most churches switched to ESV at that point.
I didn't know that! Interesting.
That sounds like a much older congregation. If the worship has a guitar, it’s probably using ESV.