A lot of people seem to believe that the result of a single fight demonstrates who is the better fighter. Personally, I don't think it proves anything (with the exception of clear ownage), except that anyone can lose a fight, even Grand Master Yoda and Darth Sidious (who each lost one in RotS). If no one can ever beat an opponent who has beaten them once, then what would be the point of a rematch?
We never got to see Yoda lose a lightsaber duel to anyone - not to Sidious, and not to Dooku - despite being over 800 years old and pint-sized with a child-size weapon. Yoda also seemed to outdo Sidious in knowledge of the force, by setting a pod in spin before casting it back at him. And although Yoda was clearly more reluctant than Sidious to use force lightning, he actually seemed to be putting out more energy in the end than Sidious (who was starting to cry out from the pain), before the force caused both of them to fly backward.
At this point, what happened was, in my mind, purely circumstantial: Yoda had just lept up to the edge of the pod, while Sidious was already in the pod, and walking toward him. When the force knocked them back, Sidious did a backward somersault and barely managed to grab the railing of the pod with one hand. Yoda had nothing to grab hold of, and fell several stories, bouncing off the Supreme Chancellor's podium and another object before finally landing on the floor.
I don't know about you, but I wouldn't have been in the mood to continue fighting myself after a fall like that. And I'm only 33; I can't imagine a senior surviving such a fall. And since Sidious wasn't too keen on letting go of that rail, I think it stands to reason that, had he taken that fall himself, then it would have taken quite a toll on his own stamina as well.
Obi-Wan actually won two fights against opponents you might expect to have beaten him. Pre-cyborg Darth Vader knew that Obi-Wan was starting to tire toward the end of their fight, and said, "This is the end for you, my master," which Obi-Wan seemed to believe. Obi-Wan narrowly avoided being cut by Vader's lightsaber when he lept backward for land, while Vader wasn't so lucky, as he was trying to jump from lower ground to higher ground and gave Obi-Wan plenty of time to deliver the one fell stroke that changed his life forever.
Obi-Wan had also been pretty well whupped by Darth Maul, but managed to pull out a victory because Maul didn't anticipate Obi-Wan getting a hold of his master's lightsaber while jumping out of the pit and then proceeding to slice him in half (not to take anything away from Obi-Wan, who deserves nothing but props for having thought of it). Less notable was the fight between Master Windu and Sidious. I actually believe Sidious was the better fighter, and he did have Windu at sword's point for a moment before Windu recovered and continued the engagement. Windu groaned and appeared to be having some difficulty before pulling out a victory against the Sith Lord with a kick to the face.
In my opinion, Yoda was truly the Grand Master of the Jedi, and more solid in his combat technique than any known Sith Lord as well. Anakin may have had the potential to surpass him, but that's left to the imagination. Unfortunately, he got jacked up badly in his first fight with Obi-Wan, and wound up having to have all four limbs replaced with prosthetics and live out the rest of his life in an air-conditioned suit with some manner of artificial respiratory equipment.
Those who sneer at the fact that Yoda scampered wide-eyed to his escape, and went into hiding while Palpatine stayed in the spotlight, are entitled to their beliefs. The way I see it, the Sith had been in hiding until they came to power. And by the time Palpatine's secret had been uncovered, he had risen to power, and had his armies hunting down the Jedi. After his fight with Windu, the Emperor made up a story about the Jedi trying to assassinate him, leaving out the important fact that he was Lord of the Sith.
As I explained previously, Yoda was too hurt to continue the fight, and had just enough strength to get away. In addition, Sidious had blasted his lightsaber out of his hand, and it would probably have been a bad idea to go looking for it in all the rubble, while Sidious was unhurt and still in the room with him. And now, the two surviving Jedi found themselves for the first time at odds with the "powers that be," and had no choice but to go into hiding themselves. Makes more sense to me than, "Yoda got scared, so he ran and hid." Remember that it was Yoda chasing Sidious right up to the very end, when he got hurt.
While it's true the Sith may have a slight edge in the fact that they feel no restraint against the use of force lightning and other abilities, every single one of them has lost at least one match in their prime to my knowledge. And furthermore, anyone who lives his/her life for evil has a crippling weakness in their underestimation of that little thing called karma; the world has more people gravitating toward kindness than wickedness, and no one can defeat the whole world (or galaxy, in the case of Star Wars). Salute!