Iran by a mile and a half. They don't behead people for Sorcery, Witchcraft or fund Salafist Terror Groups all around the world. Iran is by far the lesser evil.
How is that different from what Iran does? Just because Iran isn't completely possessed by religious extremism doesn't mean that they are somehow less worse.
Iran has been sponsoring terrorism across the globe, for many of the same reasons as the Saudis, for decades.
Also, on the execution issue:
https://www.theguardian.com/news/datablog/2016/jan/04/executions-in-saudi-arabia-iran-numbers-chinaIran is just as bad on executions. As the article notes, there are differences in population, so naturally Iran will, usually, have a higher number, but it is important to note that
42% of Iran's executions are for drug offenses. (Similar to the Saudi numbers on that).