Joseph Smith did have a progressive current in him; his support for abolition, the early practice of sealing as a more libertine elopement practice before the trek to Utah, and other progressive policies do stand out.
Now the worst has to be Brightam Young in its early history and Ezra Taft Benson afterwards. Brightam Young had not an inkling of a moral or changing leader and was a standard autocrat cult leader who brutalized the Native population, non-Mormon pioneers, and dissidents to his rule of Utah Territory/Deseret. Most of the conservative aspects of Mormonism lie with him. The latter meanwhile created the Mormon
Right.
(Honestly, Mormon Stories is a great resource for learning about LDS theology, news in the Church, and Utahn/Mormon culture—check it out)