Sorry for the long post, but you wanted my full analysis dwid.
I'd compare McGuffie's style to Reggie Bush (slightly less top end speed, slightly more burst; "potential" for more power). Other guys he might compare to are Darren McFadden ("currently" less power, but with a better burst). Joe McKnight is another great example of how Sam would compare; maybe the best example. Sam's that type of body type and all those other guys went/are going through the process of adding 10 or 15 pounds or so in college.
The other runner from Michigan, Michael Shaw, is similar too and I was also very impressed with him. The area that Sam is a cut above the rest from all these guys though is how fast he reaches top speed. He makes his first cut from the backfield and then just like that he accelerates to the hole and past the tackler.
Rex Burkhead has nearly equal agility to Sam; I was very impressed with his agility, but doesn't have as much burst or speed. Luckily for Rex he fights for yards like a junk yard dog and he could be an elite runner in college also. Mike Trumpy of this year is also the cream of the crop in elusiveness (not quite as agile as Sam, but slightly better power), but he also doesn't have the "burst" of Sam.
Brandon Wegher's agility is good, but definitely not quite at the level of Sam or the guys in the first paragraph. Wegher's one of those guys who is "very good at everything", but doesn't blow you away in any one particular running style attribute. Wegher is a "very good prospect" though when you consider how balanced he is overall as a runner and top 5 for this year IMO.
But dwid, Sam is definitely a Scat back. He cuts and hits the hole like lightning when he sees it, but he can really make guys miss in the second level when he gets his wheels going. He barely slows down at all to make his cuts in the open field.
Sam is a mix of darting and slashing styles IMO. Most white RBs I see are darters, but Sam can literally bounce cut off two legs without slowing down much at all. I'm not saying that darting isn't a very effective running style; it is actually the more common one, but that few guys can bounce the way Sam does and just take the defender completely out of the play in the open field. I think the darting style favors the one cut and go style which is great for zone blocking schemes and helps as a north-south runner who moves the chains. But Sam can do both and is one of those rare types that can consistently break long runs.
The record for most 30+ yard runs in a season stood until this year all the way back to when Jim Brown set the record with seven. This year DeAngelo Williams had 8 30 yard runs. In truth this ESPN utter garbage about how every white RB can't make guys miss in the second level or have the speed to break long runs is proven untrue by the fact that the NFL should really be testing a 25 or 30 yard dash when you consider that eight 30 yard runs in a season is the record. Gale Sayers record was 6 and Barry Sanders was 5 I believe.
Also ESPN will outright fabricate and say that any of the top black prospects have that mythical hip wiggle to cut in the open field without slowing down when these guys are VERY few and far between, but McGuffie is one of those very rare breeds IMO.
The only area of Sam's game that isn't elite is his power; which he can improve.
That hell of a program at Michigan didn't help him by throwing him to the wolves in the first two games without blocking, and having him return kicks after having two concussions was very irresponsible.
He looked absolutely great in the Notre Dame game and that is what he could be capable of every week once he feels comfortable and gets even average blocking. If he can add 10-15 lbs. and learn to fall forward better when hit Sam will end up being an elite yards per carry guy, but of course this is mainly attributed to his home-run threat and in-space ability. Edited by: ToughJ.Riggins