[Dark Paladin X]

What makes Accelerator so interesting is his character development from a villain to anti-hero:

Spoiler for analysis of Accelerator:

Accelerator starts of as a cold ruthless level 5 esper who seeks to become the most powerful esper (level 6) by killing 20,000 MISAKA clones. However, in the "Last Order" arch, at the time after Accelerator got defeated by Touma, we see more of his development of character and a slight change of personality. We are introduced to Misaka clone 20001, or "Last Order" who constantly follows Accelerator around. It is Last Order along with Accelerator's traumatizing past dealing with bullies, secret agents, and even the military that helped changed his personality. When Accelerator was given the option to kill Last Order in order to stop a computer virus implanted into her, he decided to use his powers and risks his life to save Last Order and erase the virus.

On the side note, I've repeated so many times, but if I think many may agree that Johnny Yong Bosch fits perfectly to voice Accelerator:

Spoiler for Code Geass and Bleach:

Bosch has voiced an anti-hero before: Lelouch Vi Britannia from Code Geass. And as for Accelerator's laugh, I'd use Bosch's Hollow Ichigo laugh as a reference point.

You could make some counterarguments if you want someone else voicing Accelerator for a dub or if there is a better role for Bosch for this anime.