Equal in terms of super-strength. Also equal in terms of super-speed, super-agility and super-durability. I'm tempted to say also equal to Superman in terms of super-invulnerability.
Greater than Superman in terms of fighting knowledge, experience and ability due to her extensive training as an Amazon warrior and, depending upon the continuity, many, many, many more years of experience.
Greater than Superman in terms of wielding weapons, particularly magical weapons / artefacts, once again due to her extensive training as an Amazon warrior and due to her practical mindset when it comes to battle (i.e. if she judges that her opponent is a genuine threat, then she will arm herself accordingly).
But, weaker than Superman when it comes to other super-abilities such as heat-vision, super-breath, x-ray vision and, once again depending upon the continuity, flight.
Basically, I think that Wonder Woman's unique strengths are generally balanced by Superman's unique strengths. However, if one was to consider the new DC movie universe, then it would appear that Wonder Woman is much more suitable to lead the Justice League than Superman given her 5,000 years of experience as a leader and warrior.