Staley is the better option here over Barlow and Garner, IMO. You can't discount a player who is surrounded by talent. The Steelers have made a living as a run-first team. They tried to switch that around last year and got burnt for it. This year, they didn't waste time wondering if they could make it work with Amos -- they instead got a proven back that will allow them to return to playing their run-first offense. In the end, this will help open everything up. Many of you have heard the phrase that a good run opens up the passing game. It doesn't work the other way around. The Steelers learned that last year, and will rebound nicely this time around. As the Steelers lean on Staley, he'll continue to put up nice numbers.
Barlow has yet to put up a full season as the feature back, and will be the main focus of most defenses playing against San Fran. I think he'll struggle overall or will break down at some point. I know many disagree, but I'm not expecting Barlow to anchor any of my fantasy teams.