It depends on the player. My hunter, while overall has the highest k/d in my group has the lowest playing time. My warlock is second has the midrange high k/d- but since I "got gud" since year 1 my last 6-7 months have been pretty consistent with 1.9-2.2 k/d averages. My Titan... Oh my Titan. I made him to troll people in the crucible. Bubble, NBP, PC+1, and Sword. I don't care about his k/d as much as blowing off steam or shoulder charging like an asshole. Even when I die, it's funny on my Titan.