I think most of the top RB's take a "bit" of a hit this year. Alexander because of a slight decline in OL, LT because of Philip Rivers and because I think defenses started to figure him out torwards the end of the year, Edgerin James because....well that's obvious. I think Larry Johnson is the only one who doesn't have something going against him this year. And I would only rank RB's in my to 3 or 4. Only Manning in the top 5 other than RB's.
I guess as it stand right now, LJ is my choice if given the number 1 pick, with Alexander a close second. James and Tomlinson will probably have good years though, so I wouldn't make an argument against them if they were picked first.
Another question is which rookie would you pick first, and about where. Bush would be a good gamble early (probably first round) without Duece on the team. With him, I don't know. Vincy Young? I think he's going to be a bust for his draft position, but he'll probably get some fantasy points based on scrambling. It's too far away to know how to rank these guys yet. If I had to guess now, I think I would be willing to take Vernon Davis earliest....given his talent and the fact that he is playing with a young QB likely to need an outlet. Though I'd bet he's treated more as a WR, sees a lot of CB's in coverage.