Frank Gore had 2180 total yards, 9 TDs, and 61 receptions last year. If he were going to repeat or improve upon those numbers, he would be the clear choice.
San Francisco drafted one of the best offensive tackles in the draft, improved their defense, added a legitimate WR, and got an extra year of seasoning for Alex Smith. All of those appear to be positives for Gore.
The only real negatives with Gore are his fumbling, his injury history, the fact that he's only had the one good year with Norv Turner, who is now gone, and a tougher schedule.
Gore's fumbling was a huge problem early in the season. He fumbled four times in the first four games of the season before improving down the stretch. With a broken hand this year, there's a good chance that this will come back to haunt him.
His injury history is well documented. I won't repeat it here. His broken hand this preseason, though, does not help matters. While I don't think Gore was more likely than any other back to break a hand, running backs in particulr need to be out there getting contact to be successful. Gore will be sidelined for most of the preseason. That makes him a little more likely than the next guy to get hurt in those crucial first weeks of the season, during which he'll be playing his division, @PIT, and BAL. That's a tough schedule for running back health.
The fact that he's only had one good year is probably not his fault. He was injured his rookie season, and still outplayed the incumbent Kevan Barlow. Last year was his first chance to shine, and he did well. But it does beg the question, will he be able to put up the same kind of numbers without Turner? For example, Gore had 61 receptions last year. LaMont Jordan had 70 in 14 games before Turner left town. This year, Jordan had 10 receptions in 10 games. Could Gore's numbers suffer a similar dropoff, especially returning from a broken hand, with coaches looking to keep him healthy, while Smith gets better at looking downfield, and improved TE and WR targets for him to look at? Absolutely.
Even if Turner were still here, woiuld Gore's rushing numbers be likely to drop off with the improvement of his division's rush defenses? Gore had 356 yards in two games against Seattle, 261 in two games against St. Louis, and 159 against Detroit. Seattle should be much improved this season, with the additions of Patrick Kerney, Deon Grant, and Brian Russell, as well as the return to health of Shaun Alexander, while St. Louis significantly improved their defensive line with James Hall and Adam Carriker. And they don't play Detroit this year. He had 776 rushing yards in those 5 games last year, which should come down significantly this year.
Their AFC opponents this year will be from the AFC Central instead of the AFC West. Unfortunately for Gore owners, they play Cleveland in week 17, but play the physical defenses of Baltimore and Pittsburgh early in the season.
I'll let other people make the positive case for Gore. There is one. There is also a significant negative case, and it's worth mentioning.