You've got to keep in mind that when Lucas made ANH, he had no idea that Star Wars was going to become a phenomenon with 2 sequels, and after 20 years 3 prequels, and that there would be something like the internet, where nerds like me would be discussing about who was the most powerful Jedi, Sith Lord etc.
When he made the first Star Wars movie, he was looking for a great ACTOR to play the part of and aged Obi Wan, and Alec Guiness did a terrific job of the role. At that time Lucas couldn't have been intensely concerned beyond a point about trying to show Obi Wan and Vader to be athletic and highly trained martial artists as well. And the same goes for Episodes 2 and 3. Mark Hamill is not a martial artist - nor is the guy who played Vader in the battle armour ( I forget his name ). And furthermore, the vision he had in his head of the Star Wars universe couldn't have been shown on celluloid with the film making technology of the time - thats one of the reasons ILM came into being - to go beyond and revolutionize the sci - fi technology of the time. Even then, Lucas himself said when the special editions came out, lot of the stuff he had in his head was not possible to put on film in the 70's and early 80's. Only at the time of Phantom Menace with advanced technology and better budgets could he attempt to fully realize his vision a part of which was to show the Jedi and the Sith to be the powerful martial artists at the level they are supposed to be. Even so how many great martial artists do you know who are also great actors ? Bruce Lee died in 73.
Keeping all this in mind, I feel we've got to read a little between the lines and give a little license for these extenuating circumstances when we compare Maul and Vader, or Obi Wan and Vader etc. Obviously the guy who acted as Maul is a more athletic and a better fighter and looks better in combat then the guy who played Vader - but here we are comparing characters, NOT the actors who played them. If we look at it that way, Vader DOES have the highest midiclorean count of all the Jedi, he was the only Jedi ( albeit fallen Jedi ) with the strength to destroy Sidious even though already old and past his prime and his hand just cut off in a duel. Plus as the story goes Vader was responsible for the destruction of ALL the Jedi except 2 ( although quite a few die on Geonosis in AOTC ) - Maul on the other hand couldn't even handle 2 Jedi forget ALL the Jedi. We haven't seen Vader in HIS prime and that will happen only in Ep.3 - for which I'm sure Lucas will have something special planned. I'm sure we're going to see a formidable warrior with great fighting abilities in single combat and also WAY more scarier then the original Vader AND way more powerful a Sith Lord then either Maul or Dooku. Of course all this would have to happen AFTER Obi Wan slams Anakin into a burning pit, and Anakin ceases to exist and Vader, Lord of the Sith is born.
Also in the Obi Wan / Vader duel in Ep.1 I think Obi Wan was slowly and surely being overwhelmed by Vader - it wasn't really an equal battle - I agree with the point that if it was equal and if Obi Wan really felt that he had a chance he wouldn't have sacrificed himself.
Sorry for rambling on so long - I'm a little new at this Forums thing.