Here are my RB rankings, along with my pre-draft rankings for the 2014 & 2013 draft classes for context.
My rankings are roughly 80% number crunching and 20% my opinions.
The 80% that's number crunching includes things like what's in 
this spreadsheet. In decreasing order of importance:
Athleticism: 40 time, vertical, broad jump, and to a lesser extent the agility drills
Size: weight, and to a lesser extent BMI (low is bad) & height (tall is bad)
Elusiveness: yards after contact & broken tackles, from 
my tracking & Greg Peshek's
Production: long runs, short yardage/goalline success rate, receiving, and other stats
Age & Workload: younger is better, non-RB1 workload is negative
The 20% that's my opinions includes things like:
Manual adjustments: giving points for relevant things that aren't in the numbers (e.g., adjusting Abdullah down for bad pass blocking), or where the numbers seem misleading (e.g., adjusting Gurley up because his elite 
yards after contact per carry suggests that my Hard to Tackle Rating is underrating his elusiveness)
My impression: a 0-10 rating of how good a RB looked when I watched him play
Finger on the scale: adding (or subtracting) a small amount to a RB if the rankings that my number crunching creates look slightly off (mostly to reorder tightly packed players based on my guesses about who is a better prospect)
These things all get entered as numbers, and the result is basically a weighted sum which outputs a numerical rating for each player.
For the rankings below, I've put the 
2013 & 
2014 draft classes in the same order that I ranked them before their NFL draft (which I posted to the Shark Pool then), because it seemed most relevant to compare players at the same stage of the process. (This makes things slightly tricky, because I kept tinkering with the numbers after the draft and now the numbers that I have in my files don't quite match up with those rankings. So I've had to slightly fudge the numbers in order to put them back in the order that I posted, which is not ideal for the cross-year comparisons. If two players in different draft classes are close to each other & in the same tier, think of them as similarly rated - don't read too much into one being ahead of the other.)
Enough background; here are the rankings:
2013    Eddie Lacy
2015    Todd Gurley
2015    Melvin Gordon
2013    Christine Michael
2014    Carlos Hyde
2014    Lache Seastrunk
2015    Jay Ajayi
2014    Tre Mason
2013    Giovani Bernard
2015    Ameer Abdullah
2013    Knile Davis
2014    Jeremy Hill
2014    Jerick McKinnon
2013    Jonathan Franklin
2015    Duke Johnson
2015    Tevin Coleman
2014    Bishop Sankey
2013    Marcus Lattimore
2015    David Cobb
2015    David Johnson
2014    Stephen Houston
2014    Henry Josey
2013    Zac Stacy
2013    D.J. Harper
2013    Le'Veon Bell
2013    Cierre Wood
2013    Kenjon Barner
2013    Montee Ball
2013    Latavius Murray
2014    Isaiah Crowell
2014    Andre Williams
2014    Charles Sims
2014    Dri Archer
2014    Devonta Freeman
2015    Karlos Williams
2015    Cameron Artis-Payne
2015    Josh Robinson
2015    T.J. Yeldon
2015    Corey Grant
2014    David Fluellen
2013    Treavor Scales
2015    Jeremy Langford
2013    Michael Ford
2014    Robert Godhigh
2013    Matthew Tucker
2015    Mike Davis
2014    George Atkinson III
2014    Terrance West
2015    Michael Dyer
2014    Tim Cornett
2013    C.J. Anderson
2013    Andre Ellington
2014    James White
2014    De'Anthony Thomas
2014    Lorenzo Taliaferro
Rough labels for the tiers:
Guys I like a lot: Lacy through Hyde, including 2 RBs this year: Gurley & Gordon
Guys I like: Seastrunk through Davis, including 2 RBs this year: Ajayi & Abdullah
(Awkwardly between tiers: Hill & McKinnon)
Guys who have a decent chance: Franklin through Archer, including 4 RBs this year: Duke Johnson, Coleman, Cobb, and David Johnson
Guys I can't rule out: Freeman through Taliaferro, including 8 RBs this year: Williams, Artis-Payne, Robinson, Yeldon, Grant, Langford, Davis, Dyer
The last two tiers are pretty tightly packed, and the order within them for this year's RBs could easily change (especially for Coleman & Cobb, who have pro days to run at). RBs not listed (like Javorius Allen) probably didn't make that cut, unless they're non-FBS or didn't get many carries this year (in which case they might just be missing from my data set).