Strictly from a value sense, there are only a handful of players that have seen their cards go up. If you want to invest, get a mutual fund. I'm not being glib, it's just that even Gretzky autos are going down in value. If Gretzky cards go down in value, who do we look to for an up arrow long-term?
Kopitar and Zetterberg are both poor investments, in my opinion, for the simple fact that they are European. Once they retire or simply move back to Europe, their cards will likely crash.
It's the reason Crosby's cards continue to soar, and Ovechkin, although arguably the better player right now, is second fiddle.