I don't think "Evil" is a cause that people actually devote themselves too. I think Neutral Evil is ultimately the most selfish of the evil alignments because it's evil for it's own sake. You care about yourself and your own desires and pleasure before anything else. You may use or hide behind the law, or ignore it altogether depending on the situation.
Lawful Evil is just as evil, but they prefer working within a structure - whether legal structure (evil bureaucrats, slavers, lawyers, etc.). They may not be more "evil" in an absolute sense, but they are more dangerous because they are more likely to work as part of a larger group and create institutions to support their goals.
Chaotic Evil is more dangerous on an individual level. Then tend to go for the more "hand on" approach to committing evil acts. The personal touch. They may lead a group (if they are the charismatic type), or be part of a larger group that caters to their particular world view, but it a tenuous relationship with no sense of loyalty. They tend to make a power play for leadership or just get bored because things are taking to long and go do something else. "I was part of a kidnapping ring, but negotiating with the family was taking forever. I wanted to switch to highway robbery but the other guys objected...so I killed them, killed the hostage, and killed and robbed the hostages family. Life is good."