If i just want marks (why, I don't know, gotta stay capped i guess) then I speed run. If I got new gear and need to level it, then I like to kill as many as possible. There is a balance between killing MOST mobs and going on some ridiculous tour to kill every possible mob. The best is when 2 speed runners race to hide under the platform (Archon Priest) or under the ramp (Valarus T'urac) and proceed to do almost nothing except make s'mores next to the fire as they camp and play with each other, ignoring the boss, the adds, and absolutely slowing down the entire run.