I suspect that the G.P. will rank them Super Reflexes, Willpower, Energy Aura, but I would personally rank them Energy Aura, big gap, Super Reflexes, big gap, Willpower.
Super Reflexes is an I win button for casual play, there is no denying. It's pretty straightforward to soft-cap your defenses and max out your defense debuff resistance, so you will generally only be defeated when either sheer numbers overwhelm the RNG and you breakdown, or you run into something that is designed to work around defenses. Your secondary defenses (like resistance, healing, etc.) are minimal.
Willpower is the monarch of set and forget; once you have your toggles going, you will be set for the vast majority of content and it will be layered mitigation, so you've got some defense, some resistance, some healing. The problem is that it is very easy to get over your skis with Willpower in the endgame, and the T9 is not a very good power to hit when you get in trouble. For casual content, it's awesome, but it's also very easy to faceplant in end game.
Energy Aura is a much more active secondary, and has a lot of active tools to manage your character over and above protection, namely endurance recovery. It probably has a much higher learning curve than the other two, but rewards that learning with performance. I wish the defense power didn't provide stealth, but it is what it is.