This is really going to depend on where Pitt might go in the draft. Looking across the football landscape right now, some (all?) of the best and most productive backs are Sophs and Juniors (Petersen, Snoop Stewart, Slaton, Hart, Pittman). Garrett Wolfe obviously leads the Seniors. If Pittman were to come out, I think that there's every reason to expect that he'd be one of the first five backs picked, in which case he goes. Running backs love to go early if they can, because they take such a beating. At one point, the number people pointed to was eight years as a starter in the league and you're done. Depending on injuries and durability, that can be six years or less. If you can skip one year of college ball, that's worth millions.
Having seen what we've seen this year, he's a second rounder at worst right now, IMO.
As far as the Wells vs. Pittman argument, I think we don't have one. :) At this moment, Pittman is turning out to be better than almost anyone expected. He's really grown as a back, and made progress every year, unlike some other guys we had. I can remember the arguments back a few years ago on that site which shall not be named, about RB development or lack thereof. A lot of those chicken little claims can be laid to rest now.
It's also a good idea to bring Beanie along gradually, without putting too much pressure on him. He's going to be a great one, that's for sure. Five to ten reps a game is enough to get him some meaningful time, plus it keeps Pittman well-rested. As mentioned, I want to see how he looks blocking and picking up blitzes. I'm also encouraged to see him being worked into the passing game.
If Pittman does leave early, I'd expect Mo Wells to split carries with Beanie next year. He's making some good progress, and I think that he's going to be a much bigger part of the offense down the road. Smaller stature backs have been successful in the Big Ten in recent years, so I don't buy into the argument that you've got to be a 240 pound bruiser to get it done in this league. He showed some strength in the Cincy game, and he's going to be even stronger a year from now. I like the potential of what he can do.