This is actually a nice debate. You have two very different players in Walton and Scarlett. I'm glad we got Mark and I was crushed when we lost Scarlett. ****, I even lost all my rep betting on his recruitment. Who ends up being the better player may tell us something about what what is important to success.
As to athletic ability:
Scarlett is an elite athlete who has that extremely rare blend of size and speed. Does he play fast? I think he did during his senior season. Does he use his size and run with toughness? Remains to be seen. Mark doesn't have the same freakish build as Scarlett, nor does he have the same speed. Has Mark already noticeably improved his body? Yes. Has Scarlett? Not sure--don't follow UF. Who has the edge in lateral quickness? I think Mark. Scarlett has looked stiff at times--but lateral quickness is not his game.
As to skillset:
Pass pro is nearly 100% based on desire. Mark is hard nosed kid who is not afraid to get run over is pass protection. Mark is a football guy--he loves the game. His performance against Bolles (a ridiculously successful, tough and hard nosed opponent) tells you a lot about his unselfishness in that context. Scarlett? Not sure, but I can't imagine him being tougher than Mark in that context. Scarlett has quite the edge physically, though. He is a thick, strong kid who has the bulk to consistently take a beating in pass pro. Mark excelled as a receiver in HS, and he has the quickness to be a nice route runner. I'm not sure I can say exactly the same about Scarlett, though I can see him creating trouble in the screen game.
As a runner, I want to see some more of Mark in a multiple offense (aka pro-style). In terms of style, and not necessarily success or ability, I see him as a mixture of Edge/Clinton. He has the upper body lean and stiffness of Edge to be a tough inside runner, but he seems to have the the frame and slashing ability of Clinton. I want to see what he looks like in a year. Scarlett reminded me most of a Willis type player. He has the speed and size to break an initial tackle and be gone. A unique home run threat.
As to mental makeup:
I don't think there's any question that Mark takes this category. Mark has been through a lot. He's hungry. You already know he's a hard worker. His body has already changed. He worked hard to reclassify. He loves football. He's a hardcore football guy. He's a football player all the way thorough (kindof like Jaquan). He's a 'Cane.
...my 2 cents.