Here is a list of reasons why ODSTs are more bad ass than Spartans:
01)Marine Corps
02)Semper Fi
03)they don't need military grade steroids to be badasses
04)no mommy and/or daddy issues
05) orbital -blam!-ing drops! Feet first! And no fancy armor to protect them while they do it.
06) more personality than a brick. Suck it Master Chief
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The Rookie had more personality than the Chief, and he didn't even say anything throughout the whole game.