Golden Bullet
SHD Exposed
Guardian
Hollywood
Reanimated
Polarity Switch
I started playing only recently, so I've played only Golden Bullet, Polarity Switch, Reanimated and Guardian.
Of those four, I found Polarity Switch to be by far the most interesting, followed by Guardian. Golden Bullet, while fun, didn't provide much challenge.
On the other hand, this may all change as I further level up my character. It's not been until the last couple of weeks I've been regularly playing with all five directives enabled (usually at Challenging when solo, and Heroic when paired up with a friend) and better learn techniques for dealing with each particular event.