Personally, the lightweight is the best body type by far. Its fast, takes advantage of the parkour system to it's fullest, and in the hands of someone who has say, mastered Mirrors Edge, it's speed and agility can be a dangerous weapon in of itself. Numerous times I've avoided dying by sprinting into a wall, "bouncing" off of it and landing into a slide to trip the poor sap, leaving me enough time to finish him off. And if your a medic "like me" and are taking advantage of perks and HCP's your hp should be at 5 bonus pips, doubling your health. This, pared with a good gun and good aim, could make you extremely dangerous.
On another note, I personally use the CARB-9 with various attachments (not gunna tell, least I let you guys copy me :3) and the Sea Eagle Pistol.