Well, I\'m no martial artist... Heck. I can\'t throw a punch without straining something. X_x. But the way I see it, they\'re both perfectly equal. Wether or not Kendo or Kensi is stronger depends on who uses it. Different people have different styles, and different ways of approaching things. Also, depending on the situation, you may want a single, strong blade, or two small, speedy blades.
Lets say (this is just an example, now.), you were going to fight a group of ninjas. Kensi would be better because you can use the two blades to defend yourself on all sides and attack in multiple directions.
Now, lets say (Also just an example.), you are fighting a giant ant, or some other demonic, well-armored creature with a small weak point somewhere... the long-blade would be better suited to striking that weak point. twin small blades would not help much here, since the weak blades would probably shatter or not be able to penetrate with the force of one hand. But a single, two-handed, powerful blade would be perfect.
Anyways, once agian, those are examples. Don\'t expect to be fighting any giant ants or octopuses...