Steady and almost nothing else, including any officers I hire or pick up. In theory Cautious officers would be the perfect choice for ships with ATC (Paragon, Arachne from SWP), but the AI fails utterly at handling ships with bad flux dissipation, and sticks them out in front of my deployed ships formation - which is well inside enemy weapons range which gets them overloaded and killed every time. I optimistically assume that micromanaging such ships with separately placed orders with regards to their range but I doubt it will work as intended.
Timid is useless. Aggressive is situational, which is why the toggleable Full Assault order is an amazing addition which works so good if you know when to hut it. Aggressive officers are also a good choice for overdriven ships. Reckless is a liability, but it works well for AI faction fleets who would thematically make great use of such doctrine, like the Luddic Path.