Light side choices make more since in some ways, as such my Sith always ended up more light than dark, unless I pick just for DS or LS points in game. As for Sith VS Jedi it comes down to this IMO Sith have feelings and Jedi are boring lumps of unfeeling stone.
As for Light and Dark we never been told what the force is or how it works, all we are told about is belief system. I believe the force don't really care if your light, dark, grey or a rainbow (some groups in Star Wars universe think its coloured) nor do the types of powers used.