I don't think it's fair to ask this question yet. So far there has only been CGI trailers of FFXVIII, so we can only assume from what Nomura explained for his vision of FFXVIII.
I think that if they can actually implement their vision of a Darker themed FF, coupled with a battle system and game style closer to the KH games, then I don't see why FFXVIII won't be the better RPG, but we really can't say yet.
Edit - Can people please stop turning every single thread into PS3 vs 360? That's off-topic and flamebait.
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