what the hell are you talking about about the PS3 being twice as powerful as the XBox360? this is simply not true. The only trustworthy comparisons I've read were from game developers who said that for what they had seen, both systems had an about equivalent amount of raw power, now, we'll just have to see which one can be exploited the best and for that, we'll have to wait at least 2 years, as it's always been (look at the games released during the first year of the PS2 and you'll swear these were PS1 games).
Nobody can say which one is better now simply because nobody owns one. In the end, it will be a matter of personal interests and will probably mostly depend on your opinions about the companies and the games they'll release
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PS: as for me, the only system I'll buy during the release week will be a Nintendo Rev because I'm a 100% sure this one will be different and fun right from the beginning. I'll wait for something like Final Fantasy XIII before buying a PS3.