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I always see Superman as much more physically stronger and durable. If Flash's schtick is running, Superman's is being the strongest, toughest, and best flyer around.
But WW is a far better fighter and warrior and no slouch herself in the strength department. So he'd clearly win the fight, but is going to take a serious couple hits in return for it being a lock-in for him and him not wanting to repeat the experience (even if he'd technically win again).