I respectfully disagree. In my opinion, the most important places to put money are the Offensive and Defensive Lines.
While there is no point in comparing talent levels between Bush and Ferguson, due to the differences in the position they play, I feel taking a Running Back over a Left Tackle is foolish 99% of the time, in terms of the early round draft. There are exceptions, of course.
Let's face it, Running Back is the position in football with the shortest "life-span," if you will. Running Backs get beat up, early and often. Especially fragile backs. Would you rather plug in a Left tackle and then forget about the spot for a decade, or a RB where every play might be his last? Hell, just look at the runners taken in the top 10 since the 1990 draft year.
Edgerrin James, Ricky Williams, Curtis Enis, Lawrence Phillips, Tim Biakabutuka, Fred Taylor, Jamal Lewis, Thomas Jones, Ki-Jana Carter (#1 Overall!), Marshall Faulk, Garrison Hearst, Jerome Bettis, Tommy Vardell, and Blair Thomas.
I'll leave Ronnie Brown, Caddy and Benson out, since they are still "fresh."
Out of those runners, with plenty of time to evaluate them, would you take any of them #1 overall? Faulk and Bettis, sure. A few others have had decent careers, but aren't worth the #1 spot. But just look at the guys with short careers, riddled with injuries, or those who were busts. Quality can be found at RB later. Even Emmitt lasted to 17 when the Cowboys drafted him. Barry Sanders, quite possibly the most exciting running back to ever play, was picked 3rd in the '89 draft. Theres two of the best backs to ever play the game, and they didn't go #1.
While this is certainly a personal preference, and I by no means expect my thoughts to be "right" or "wrong" in terms of drafting, I wouldn't draft a RB over a LT early unless it was a glaring need for my team.