To tell you the truth no one can answer that question for one main reason. All the character classes have strenghts and weaknesses. So there is not one main class.

rangers are great at long range but cannot survive a hard melee. Hunters are great at close range but are can be hindered in boss fights where long range is needed. Forces are weak in close range and long range weapons but can use techniques much better than all others.

You could break down the others too such are humans are good well balanced but have less than this char or that. Andriods are the strongest but cannot use techniques,but they can see traps.

You can continue on like this all day. The best advice you can recieve is find a class you like and use it otherwise your not enjoying the game to the fullest.