What are the scariest rides in Knott's Berry Farm?

Ok, I'm taking my boyfriend to knott's scary farm in a couple weeks, and he is afraid of roller coasters. I want to ease him into roller coasters by taking him on them one at a time, in the best order possible. What is the order of the roller coasters there from least scary, most comfortable coaster, to most scary, most exhilarating coaster? I know he'll like them eventually, but he's afraid of heights, and he's very apprehensive.