I would choose Sith.
In my opinion, Sith are force users that draw strength from personal ambition and passion, while Jedi draw their strength from creating (and enforcing) emotional distance and (on the average) sublimating ambition in favor of cohesion.
Jedi (Light-Side Force users) draw their Force aptitudes from nature (and to a degree, the intuition of the Force). Sith take hold of their Force aptitude through more internalized control of the Force.
In my observation, the greatest Sith Lords are those who own the responsibility of their powers and then make calculated strides toward their driving ambitions. In my eyes, stronger Sith usually have the traits of great leaders and embody the successful pursuit of ambition.
The price of freedom is eternal vigilance, and as long as I do not squander the freedom my passion, power, and victory grant me...I stand to see my vision realized.
I like this, and so...chalk me up to the Sith.
(Sorry for unbalancing the poll)