what game should i get killzone 2 or halo 3?

[Gilgamesh]

If all your friends play both and you think both are good, then why don't you get both.

Halo is the best FPS on Xbox 360 and Killzone is the best FPS for the PS3 so I'd say get both.

(You can likely find a cheap copy of Halo 3 since it's been out for 2 years.)