The game is written better for LS characters IMO, though playing DS can be really funny at times as long as you stay disconnected from your characters' actions. And while the full complement of LS powers are overall more useful IMO, Force Lighting/Storm and Choke/Kill have that nice evil kick to them.
My next game is a DS Female Consular->Sith Lord with a Double-bladed saber. I want the three Dark Lords to feel the true power of the Dark Side....hehehehe.