POC Storm Shadow is one of the nicest Joe figures they've made, but he's got this weird desert vibe going on (because of all the deserts in Japan, y'know). Next, I'd say Renegades Storm Shadow is best; he comes with interchangeable heads and sashes so you can display him as the Renegades or classic version, and is a downright awesome figure. If you want the first 25th Anniversary mold (which isn't bad at all, just eclipsed by later sculpts), I really like the black-garbed "Ninja-Ku" version, even though he's not really traditional. (Ninja-Ku was a repaint of SS for a Brazilian line, who was an African-American guy, but they just made him be Storm Shadow for the 25th line... don't ask.)
Zartan... I don't know the HOH version (I passed on all of those because they were too similar to earlier versions and cost too much, though I got one or two at Marshall's eventually). The POC version is really nice, but, uh, he's basically Raptor with Zartan's head.