honestly? windu loses to sidious in a long drawn out and epic fight, though windu fairs better then yoda sheerly because he isn't as arrogant as yoda and doesnt let idea he's jedi warp his perception of fight. This was probably biggest reason yoda lost he underestimated sidious where as from what we saw of windu he didnt and he was much more serious in his battles. I feel yoda was stronger in the force, maybe he was even better with his saber BUT windu just has a much better fighting mentality and he's a no none sense kind of warrior. plus his saber combat style is much more aggressive and probably throw sidious off his game.
Windu could take on Sidious for so long mainly because his Vaapad style could reflect Dark Side of the Force.