This question seems to have everyone up in arms, which I don't quite understand. No one knows who will be the Tampa Bay Buccaneers' starting running back yet, but I can make an easy prediction: Doug Martin will beat out Legarrette Blount. First-round picks always have a leg up in competition in practice, but that's not just why Martin will win the starting job. He will win it because he's a more versatile running back, who can also be a factor in the passing game.
Blount, meanwhile, is a running back who runs the ball and does little else. He has the physical ability to be a good pass-blocker, but he only got a few chances to do so in the past two years - and there's a reason for that. More importantly, perhaps, I don't think he'll ever be a quality receiver out of the backfield: he does not have the ability to make the first man miss in space, which is a necessary component of being a good dump-off receiver.
To me, it's almost a foregone conclusion that Martin will win the starting job. But that's not a real relevant observation. 'Starting' means nothing more than being on the field for the first snap of the game. Doug Martin will get that first snap, and he'll get almost all of the snaps in the passing game. But that doesn't mean Legarrette Blount won't get his chance as a runner. I would look for an Ahmad Bradshaw-Brandon Jacobs distribution of carries between Martin and Blount respectively. Most teams have two backs who receive a significant amount of carries, and both Blount and Martin will get theirs this year. The question of who will start is a lot less relevant than how that distribution works out.