This. The other thing to look at is improvements over new stuff. For instance, TOR has the hyperdrives, but are they as fast as in the OT? I think an ISD would destroy a Hammerhead easily. Look at firearms as an example. We are constantly making improvements to firearms, bullets, cartirdiges, etc. At the core however it is fundamentally the same, an explosive charge propel metal along barrel at high velocity to inflict injury upon soft tissues. Some sources cite the Chinese having working firearms as early as 700 AD. That's 1300 years we've been using the same basic principle for firearms, though it has been improved. The internal combustion engine could serve as another example, sources citing the first ICE to be around the 13th century. That's 7 centuries of improvement, but again pretty similar execution. You can see a lot of these paralells in our tech, where we are constantly "tweaking" it. Star Wars tech for a lot of people would have hit the top so to speak. FTL travel gets the job done so it sits in the "tweaking phase" where people just keep pushing it (like the classic "She'll make .5 past lightspeed". If you look at it that things are getting tweaked, but brand new ground breaking things are invented, then factor in constant strife and it seems the Star Wars universe isn't that far fetched or stangnant after all.

Juyo, I think I might have to go with Palpatine/Sidious. He went toe to toe with Shaft Windu (and by some accounts was just baiting him the entire fight) and seemed to use a similar style. Everything seems to point to Vapaad being like Juyo in physical form, references that Windu "completed" Juyo and stuff like that. It wasn't the defense you saw from Obi-Wan, the power strokes from Anakin, or the delicate strikes of Count Dooku. While incorporating some flips etc, the attacks from Sidious seemed much more vicious than anything from previous duels we'd seen. The only mirror to the brutality and wanton destruction he exhibits in that fight seems to be Windu. Maul was good, but Sidious was better I think. As for Shien/Djem So, I definitely think it'd be Anakin. That form seems to be all about raw power and he has that in spades. He overpowered Dooku with it, I think some books mention he burned Dooku with his own saber when he blocked a strike from Anakin (could be wrong). He was pretty even with Obi-Wan (master of defense), but Anakin had no defense against script. Finally....Luke Skywalker, who everyone loves to hate on, basically formed his own "style" since he had no real formal in lightsaber combat. Most believe he mirrors Shien the most, so if you shoehorn him in anywhere it'd probably be into Form V...making him the greatest ever with Shien.

Meat to quote EndMoztGrim to answer his question as well... Obi-Wan, after witnessing Qui Gon's death noticed the flaws in Ataru (the form the two of them used in episode 1 and also used by Yoda) and began to study Soresu to compensate for the lack of defense with Ataru. Ataru requires more exerted energy for all the flippy, spinny, look at me look at me moves (see Yoda in Ep II). Obi-Wan noticed this exacted a high toll on most users, leaving them unable to maintain Ataru's pace for long periods (resulting in the afore mentioned lack of defense) and switched to Soresu. Soresu is generally considered THE defensive form as it focuses almost exclusively on defense, waiting for an oppurtunity, then counter attacking. Best Example is probably Grievous fight in Episode III where Obi blocks, then slides the saber and severs Grievous's hand. Very defensive with slight to no wasted movement and energy. Obi-Wan is a master of Soresu, and in some cases regarded as THE master (by Windu) which implies Obi-Wan is the greatest practioner of Soresu to ever live. That last part may be just because Obi-Wan is my favorite jedi, but he was one of the best with Soresu without a doubt.