In KotOR, if you're talking plain damage, dual Baragwin Assault (vibro) Blades were the best, except perhaps against dark-siders, which seems irrelevant since the game considered Malak neutral (and thus everyone except maybe Bastila I would assume). But some lightsabers will probably surpass everything else in TLS, as they should.

 

For style though, I would have to go with dual lightsabers, one blue and one green.

 

For actual fighting, look at fencing: dual, with short off-hand.

Single saber,

Single saber,

double bladed

Single saber,

I prefer the dual sabers because I can use more crystals and therefore if I use the right ones I can have a stronger saber but it usally only works if you have the feat that lets you almost remove the dual weapon penalty