Welcome to LF The Witch King
I would getting better with the Scout (sniper) and Arc (heavy weapons); those are the ones I use
But really I would say you have to play multiple matches, each using a different class. I would make the AI difficulty hard seeing as that is the closest to online opponents you can get. Additionally, I would play the matches on the same map. After each match I would then write down what you liked and what you didn't like about the class you used; and when you are completely done decide which class (or classes) you like the most/ you did the best with.