Absolutely, positively, and without a doubt, *Rescue*.
Rescue teaches you the skills and procedures for effectively rescuing divers in need, but more importantly, Rescue teaches you how not to need to be rescued. Spotting the signs of oncoming panic and cutting it down before it can get a hold of you is but one example of what Rescue covers.
Once you're getting into deco, you reach the point where to be "safe" you *must* solve your problems underwater. Rescue will give you tools to be able to more effectively spot problems earlier, where they're much less complicated and much more easily addressed.
(If you've never had a dive where you had the crushing urge to bolt and had to grab the biggest mental sledgehammer you have to bash your visceral instincts into submission so you could deal with the problem, I certainly wouldn't advise anything like deco. You needn't have an actual incident, but something like overexerting yourself and having to use all your mental power to will yourself to breathe deeply and calm down will certainly give you perspective to handle when you feel something bad start to happen.)