First step only helps when your player is at a dead stop (or close to it) so unless your FB is catching passes, I don't think it's overly useful for a FB. Also, since it's not a natural SA, it will take a while (and resources) to get it to a useful level.
I'd definitely pick lead block, which is the best FB SA, along with Power Thru.
I'm not that high on Pancake myself so I'd holdout for Power Thru, Break Tackle % or something more useful depending on your build.