As of ROTS they are pretty much almost dead even with each a slight edge in different categories. In terms of sabers based on the deal from the movie they are even as no one was able to gain an edge on the other. The script I believe says sidious was disarmed but never made it into the movies or deleted scenes. The CANNON wookipedia for this battle explains the fight and says that neither could gain an edge and palaptines movement was hampered by the small space. It then goes on to say he changed tactics, not that he was disarmed. So this vs something that didn't even make into the deleted scenes. I wouldn't know which to go with. Actually it logical to believe that sidious wasn't disarmed as neither could gain an edge and he didn't want to be there forever during his moment of triumph so why not go for what you are best in. Also because someone beats someone once doesn't mean that they always will. Factors were against both combatants.
So with that sidious and yoda are equals in terms of sabers with yoda may or may not gaining a slight advantage.
With the force is say that sidious>yoda by a slight margin.
ROTJ sidious is definitely unquestionably greater than yoda.