Good arguments all around, I was bouncing back and forth in my opinions for a while there.
After reading all this my conclusion is simple. PT beats OR
I will play out a theoretical scenario in short story form to illustrate why,
Its a dreary, cool morning. The sun has begun to rise and a brisk wind floods the green valley. A nondescript hooded figure cloaked in brown robes enters the small cradle of pasture among the towering peaks. Another figure, wearing ratty tan robes and armored leggings, strides in from the opposing corner to meet the brown clad man. As they near, each one slows to a deliberate pace. They begin to remove the loose portions of their distinctive outfits and stop several meters away from each other. They two men draw their sabers and salute the other.
They begin to circle an imaginary spot between the two combatants. Tan clad makes the first move. They hum of his saber cuts through the morning air and the clash of the warriors blades send sparks across the space between them. The Brown clad is thrown on the defensive and, having mastered Soresu, parries each attack deliberately and precisely. Tan continues to press, carried by the energy he feels from his use of Juyo. Brown allows this, maintaining his impeccable defenses he gives ground slowly. Feeling his opponent give ground, Tan begins to drive even more, landing his blows swiftly while searching for an opening. Not finding one, and beginning to become frustrated, Tan disengages and makes several flips away to take stock of his situation.
Realizing his opponents aim to frustrate and tire him, Tan calms himself and sets himself to begin the next round with Ataru. However this time, Brown is the aggressor. He charges with a force propelled leap at Tan, attempting to land broad heavy blows. Tan's nimble Ataru stance allows him to easily avoid this juggernaut of power coming at him. Brown though, will not relent. He continues to attempt hammering blows to Tan and subdue him. Tan however, seeks to use this to his advantage. As Tan uses his acrobatics to get behind Brown's wide swings, Brown pivots. Coming about, he smartly parries and manages a smooth riposte aimed for Tan's exposed midsection. The now Makashi fighter flows into a series of moves that further pick apart the hastily composed Juyo defense. Brown transitions once again into Djem So and hammers away at Tan. By now both parties are exhausted, yet Brown is fueled by his superior force power.
The battered Tan knows now, when it seems he is at his weakest, is the time to strike. A firm force push throws an unsuspecting Brown 30 meters and Tan leaps directly behind his attack in an attempt to kill Brown in his surprised state. Brown is suitably surprised, yet his instincts in the force prevail. He rolls to his right and blasts the incoming Tan with a push of his own. Tan lands 10 meters away. Brown, having now separated himself from Brown, sets himself into a Soresu stance once again. Tan, his favored Juyo.
Now, Tan is wounded with a gash to the midsection and is bleeding while Brown likely has a cracked rib and bruised sternum. Tan assaults Brown again, this time more deliberately, and continues to search desperately for something to give. A minute passes with no relenting, no pause, no respite. The combatants are locked in a dazzling display of saber prowess. Steely determination borne of uncountable conflict and force augmented tirelessness borne of endless repetition, who will give out first. Almost inevitably,
Tan's wounds, caused by Brown's impeccable ability to seamlessly swap styles, force his body to give out first. As darkness clouds his vision, an unexpected counter-offensive by his opponent catches him off-guard. Brown's saber comes in high, blows raining down upon Tan's head. Brown finally bats away Tan's final defense and neatly beheads Tan.
In the grisly aftermath, Brown gazes upon his fallen foe. Shuddering, he moves slowly with great pain, to bury the dead, and honor a brave warrior. The survivor does not finish the shrine to his enemy until dusk. And as the sun sets on this day, so does it set on a fallen member of a powerful order, lost to a member of the generations to come who built upon and improved that which was refined in the heat of battle so many centuries before.
TL: DR (to long: didn't read)
The Prequel Jedi's knowledge of more forms allowed him more options and more ability to counter a limited opponent. Also, as you see late into the battle the thing that finally killed the OR jedi was his weaker force ability and lack of knowledge in multiple forms*. In battle, stamina is easily augmented by the force and the PT jedi easily has more force power, hence more stamina despite the OR jedi's battle toughened body.
I attempted to include the OR jedi's wisdom, reflexes, experience, cleverness, and aggressiveness in this. The PT jedi had patience, reactions, force power, and strategy on his side.
*The OR jedi who is constantly fighting will learn 1 or 2 forms and stick with them if they work, he doesn't have time or need to learn a third or fourth if 1-2 works. He gets really good in those 2 due to constant use but not much more.