Most powerful wizard?

Hmm....hard to say off the top of my head. Does this include beings that can access magic, such as demons? Or strictly people/beings that categorize themselves as wizard/witch/sorcerer?

Sise Neg or Mordru

the Wizard Mordru

The Wizard Shazam, Sise Neg, Mordru, Nabu. That's all I can think of right now.

@thekillerklok: Tell me about her.

Mordu or Sise Neg.

Othinus (Odin)

with her staff her magic is 100% effective in every possible reality.

and she can basically do whatever she wants with her magic.