It's interesting, cause I agree with Rsandee that the NTSC version definitely feels more iconic, but I feel like it doesn't really convey much at the same time. It puts most of the weight on Clank (the sidekick) than it does Ratchet, and doesn't really say much about the game itself. Whereas the EU cover does a better job on the conveyance standpoint, but is far more generic.
I suppose if we're going off "looks," I suppose I'd give it to the NTSC box-art, but in terms of the era it came out, and the need for eye-catching box-art, I'm not quite sure which I'd say is better.