The predator should never be the "hero" in a Predator movie. He isn't a villain either, he is only a force.
That said, the Predator can be shown to be doing "good deeds," such as killing the guy who is about to rape some girl, etc (although this would really be a side effect). In the same way, I would like P3 to occur in such a manner where the predator is mostly hunting scum (perhaps because those are the only people who will be able to carry weapons in a future setting or something, or maybe just for kicks, because of the demented genius) and his trophy is some scumbag, say a cerial killer/rapist/peadophile/child murderer/mob boss, etc, which would allow him to claim his trophy without the fans going nuts because he "killed the good guy".