Chief gets shit done, no real questions asked. Like a badass.
Shepard bangs his through the galaxy (and the decks of the Normandy), asking all sorts of questions, getting to know everyone and helping in lots of little knit-picky situations/fetch missions.
If I've gotta have one to save the galaxy?
Chief. Durr.
Can you imagine if Chief was calling the shots on the Citadel there at the end?