There is no doubt about Darren McFadden being the #1 ranked rookie keeper prospect for 2008. He has held this spot for two years already.  McFadden is almost as sure a thing as Adrian Peterson was last year and could be better if not for his much weaker offensive line.
The real debate, in this abnormally great year for rookie-only drafts, is the order of the next four rookie keepers. We’ll see what happens in training camp, but Jonathan Stewart, Rashard Mendenhall, Kevin Smith and Matt Forte will all have an opportunity in 2008 and any one could become the next Steven Jackson or Marshawn Lynch. You also can’t discount the possibility that Felix Jones or Ryan Torain will emerge in preseason games.
After pure talent in determining a rookie keeper’s value comes the players overall situation. Of the four best running backs after McFadden, Mendenhall clearly stands out as having the best 5 year outlook due to the combined youth and relative experience of his teammates. Roethlisberger, Santonio Holmes, Limas Sweed, Willie Parker and Heath Miller form a core averaging 24 years old, so if Mendenhall can establish himself as the lead back, he has a better chance of continuing solid production through 2012. That is, if the Steelers aren’t sold and moved to Los Angeles by then.
It wouldn’t be surprising to see Stewart have a better 2008 than Mendenhall, but Stewart is playing with aged Jake Delhomme (33), Steve Smith (29), and Mush Muhammad (65), which limits his future upside. If you take Stewart #2 overall in a rookie draft, he should be counted on as no more than your RB3 for the next two years. If the Panthers have another bad year in 2008 they may go into full rebuilding mode.
Matt Forte and Kevin Smith round out the top 5 overall fantasy rookie prospects. Neither is in a great situation, but they seem like they will get the carries on their teams. Instinct tells you Smith will be the better short-term play while Matt Forte is the patient play. Kevin Smith has a chance to do well with Jon Kitna in a last gasp type season in 2008, but after that Detroit looks pretty bad.
Matt Forte could conceivably benefit from the drafting of, or trading for a QB that could manage the Chicago offense better over the long run, but thats a very speculative bet.
Shades