A tentative stab at some tiered RB rankings:
Lache Seastrunk
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Carlos Hyde
Andre Williams
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Jeremy Hill
Devonta Freeman
Bishop Sankey
KaDeem Carey
Sleepers/Flyers:
Ameer Abdullah
Branden Oliver
Tim Flanders
Isaiah Crowell
I'm trying to keep an open mind, but I think it's unlikely that one of the 3rd-4th tier guys will jump up into the top 3. Today I'd take Seastrunk as the top RB and feel pretty decent about it. Hyde strikes me as a really safe pick. Not a super dynamic guy and he doesn't make a lot of SportsCenter runs, but he just looks like the kind of durable workhorse you could grab out of the 2nd round, plug in right away, and get 250-300 carries of serviceable performance from immediately. Very sturdy build and fluid running style. Also shows some ability to catch the ball. Andre Williams is a different beast. Not every team is going to like him (because he's basically a two-down runner only), but the teams who covet that might REALLY like him because he has some "wow" qualities as a power runner. Hulking frame, extreme strength, and deceptive straight-line speed. Not a juker and not a good open field guy. Not very sudden. Has a very deliberate, but powerful running style. He doesn't really look like Jamal Lewis and he doesn't really run like him either, but if he hits that's the kind of impact he could make. A guy who racks up yards and breaks long runs because nobody wants to tackle him. I see more "wow" factor, but also more durability risk and more bust potential than with Hyde.
The third tier is guys who could go rounds 2-4 and potentially be serviceable starters right away. I think all of those guys are flawed enough that you can't really consider them elite prospects. It's not out of the question that I could move Carey or Hill up to the bottom of the second tier at some point though. Hill has a lot of character baggage and strikes me as the kind of guy who could look bad at the combine. That event will be especially important for him since he seems like a guy who could either really shine or really look bad in that environment (whereas you can pretty much bet that guys like Seastrunk and Williams will look the part). Never really been a big Carey fan, but at some point the production has to mean something. It can't all be by accident.
The sleepers/flyers are guys that I like to some degree, but who aren't really mocked high enough to be considered major contenders for the top few RB slots right now. They're all compelling in one way or another. Whether it be as a small school dominator (Flanders/Oliver), a fallen prep star with some upside (Crowell), or an atypical but hyper athletic major producer out of a major BCS conference (Abdullah). I guess you could throw Marion Grice, Jerick McKinnon, Antonio Andrews, and Charles Sims in there too for the simple reason that they've been invited to play in the Senior Bowl.