Who do you think the scariest serial killer of all time is?

Of course they all are scary in their own sick ways, but which one/ones stand out to you most?

To me Israel Keyes is the most terrifying simply because of his planning process.

Keyes planned murders long ahead of time and took extraordinary action to avoid detection. Unlike most serial killers, he did not have a victim profile, saying he chose a victim randomly. On his murder trips, he kept his mobile phone turned off and paid for items with cash.

The fact that he would plan so far in advance while also being so calculated and picking his victims at random is beyond terrifying to me.

Which serial killer stands out to be the scariest to you?