Who is/are the most Powerful DC character/s?

If it comes down to it, the Life Entity. It's the most powerful being in the universe, is the source of life as we know it, and, if hurt, it hurts all life in the universe. The God thing didn't happen in the current iteration of the DCU, so He doesn't count, and the Watchmen universe is a different one from mainstream DC, so he doesn't either. Nor do the Endless or Lucifer, for the same reason. So yeah, the Life Entity is the most powerful. Hope this answers your question well enough.