I voted Semin, but it depends what you mean by impact. Semin could balance out our acting, but he could repeat last season. Kassian could finally realize his potential, and become a power forward with soft hands on a regular basis. DSP could come in in top shape and have a season reminiscent of a few years back with the Ducks. If all three happen, we are a serious playoff contender, and so all of them are having their own unique impact. Even if only 2 take that step, we are a serious contender, but which of those two it would be is anyone's guess. But, if only one of them made it, which would be the most likely, while being the most beneficial to the team? Semin.