There's supposed to be a "Ghost" one too I believe, it's for if you just try to avoid fighting and sneak in to the objective I guess.
Grunt seems to be very loud bang on the money people and I had ranger and kept things silent at medium to close range mostly using a sniper rifle and assault rifle, trying to stay undetected and clear every enemy out of a location without getting detected.
Have no clue what would give you the other playstyles.