I use net carbs. Simpler that way. I do eat low carb. However, if you use insulin you need to be, aware that some carb foods digest more quickly than others, which may affect insulin dosing.
Net carbs doesn't take into account the fiber in foods, because some types of fiber don't affect blood sugar. For more on fiber and why it's health in a diabetes diet, read this from MedHelp.org and the Sugar Sense app:
http://www.medhelp.org/diabetes/articles/Natures-Blood-Sugar-Secret/1822
But, the simplest way to count carbs is to just use the numbers on the label, as in this article:
http://www.medhelp.org/diabetes/articles/Your-Carb-Counting-Cheat-Sheet/2289
You can find these articles in the Eat Right section of the Health Guide (accessible from the menu in the upper left of the home screen).