It's a hard question to answer. I suppose, if pressed, I'd have to say Del Mannsfield was the strongest. He was an electric/regen scrapper, and he shredded everything. I never really paid much attention to the enhancements aspects of things, so he probably could have been even better, but I remember him being awesome. It could also have been the combinations of power pools I used. Not sure.
My most fun character, though, was my main. Safehouse was an energy/psi blaster, and he was an incredibly good time. Even though I had to kite a lot, because blapper, it was just a blast (pun not intended) to tear it up with my powers. He may have gone down a lot, but with him that didn't matter. Plus, he had a whole storyline where he was gradually turning to the dark side - actually thought of submitting the full story to a comic company. By level 30, he was a vigilante. By level 40, Scirocco had convinced him to join Recluse's cause. But, by level 50, he found his way back to the light.