South Carolina, Texas, Utah
In that order. First two will be close though.
Utah? Only if a Democratic Mormon ran.
Utah has insane population growth that's non-Mormon. It's pretty likely it will be like Colorado in about 20 years.
Colorado is only about 2% Mormon though. Yes, Utah non-Mormons are very Democratic, but I suspect a lot of that is oppositional voting. If Mormons were reduced to a minority and no longer dominated the states' politics, I'd guess the non-Mormons Utahns would start voting somewhat similarly to non-Mormon Coloradans, leaving the state still quite Republican.