McCoy. Although I don't really agree with how they arrived at that the origin of his nickname. Although his introduction (that of his ex-wife having left him with nothing but his Bones) can be seen as somekind of cinema shorthand to clue an audience in quickly of who he is. In my mind (Yes, I know... fanon isn't canon), McCoy was called "Bones" because of "Sawbones", an old term for a Doctor serving in the military in historical times. Just like "Sparks" would be an electrician or electrical engineering. How would he come by that in a future where legs aren't crudely sawn off on a battlefield? Looking around his sickbay in the Original Series, reveals a lot of antiques related to medicine like metallic operating scalpels on the wall (see Space Seed). He collects such things then and his patients presumably lie around looking at those, thinking he'd much prefer to go back to those old tried and trusted methods, than work with more pain-free gadgets.
I'd despute Scotty the most though... I think he's a different character over there and should've been out there working onboard starships, working his way up the career ladder to become an assistant Chief Engineer, before reassignment to the Enterprise. But instead is in a bit of trouble with his career, for having dabbled with transporter experiments of all things.