One question for NCR Couriers, one for Legion Couriers. Not applicable to Independent/House Couriers.
Rangers are a separate branch, so I put them at the bottom - to signify the different branch, not indicate that they are lower in rank.
Personally, my main NCR Courier would be more drawn to the Rangers - I think he'd make a good Veteran Ranger, with the black armour. He wouldn't want to be the Chief - too much admin. If the army called, I'd want to make at least Major rank.
My evil Caesar's Legion character would probably make Decanus, the higher ranks are probably a bit too close-knit to allow such a relative newcomer in.
What about your character?