What is best wedding flash For E-M5?

For use on Olympus OM-D E-M5. I want the most powerful, adjustable, bounceable flash for on-camera OR bracket use. I want to use a diffuser almost all the time, harsh light is not good. I used to shoot weddings with Nikon and Hasselblad back in the 60-70s and used a "potatoe-masher" as I called it. Now I'm retired and again doing occasional jobs. Got the OM-D with 12-50 a few months ago and it is fine. Just need lots more (diffused) light. Anyone suggest the perfect unit?