What I would really like to see is Garrett as GM. I think it better suits him. He is better when he has time to think things out than what happens during the pressure of game time situations.
I've said before that I think he would be a better GM than HC. I think his thought process is too slow, methodical and calculated when it comes to making snap decisions on the field, you can almost feel him freezing up in certain situations. He is a very intelligent guy in general though and I think he probably has a good overall philosophy when it comes to team-building (muddied by Jerry's idiocy of course) but I don't think he's really cut out for coaching.
I don't think he's creative enough to make adjustments on the fly in the condensed time frame that is an NFL game, nor do I think his personality really galvanizes the majority of personality types that are in the NFL.
I think he would be at his best working on a macro level, removed from the chaos that is an NFL game/locker room, where he's able to gather information and make thought out, calculated decisions.