A suprising number of classes are very good at 1v1 in the right hands. There is a lot of bias players thrown around when saying "x class is best". Very few people will believe statements like "mando/merc gunnery/arsenal is strong 1 on 1" (which they are, and can kill many classes, much more then people would believe), but that's not suprising considering that some classes have an easier time handling a 1 on 1 encounter and as such a lot of them are more frequent then others.
Adding my own bias to what already is, I'd say scoundrel dps may be the best, but that's just a hunch really. Other then that, maybe rage mara/deception sin/veng jugg? I'd go so far as saying merc dps too, but that's not for the faint hearted.