I gave this a lot of thought before I started my character.
As a lot of people did, in the beta weekends, I played only republic as I knew BH was going to be my main.
What I finally decided is to just let this character play out with whatever alignment it turns out to be, and not to aim for any one alignment.
Right now I am level 17 (just got to the third planet) and am just barely light.
My next two toons though will be force fed alignments.
A dark inquisitor and then a light AI or a smuggler.