Here are my thoughts as I try to sort out the RBs:
Henderson - Best Talent. Market Share very variable due to McVay. Unknown how long Akers is out. Hard for me to feel safe starting him any given week, though I suppose a Brown injury could mean gold.
McKinnon - Good Talent. Pretty good short-term market share outlook. Long-term market share very variable due to Shanahan.
Davis - Decent talent. Good market share outlook for the next 4 weeks or so. Some chance of value after that if CMac injury lingers. Ceiling is probably fairly limited even when he does play.
Freeman - Decent talent (unless he is physically a lot better than last year). Hard to assess the market share outlook, though if he is in decent shape, you would think that he could grab the backfield. If he does, then he is good all year.
Gallman/Lewis - If Freeman can't hack it or goes down, he probably gets the majority of the work. Lewis will always have a role though, and the Giants will probably be down a lot.
I think that if you need a starter right away, you want McKinnon or Davis. If you can wait it out a bit, Henderson or Freeman are stronger plays.
Other situations to consider/monitor:
Josh Kelley of course if he is still out ther
Lamical Perine
Chase Edmonds
Gio Bernard
Jordan Wilkins