I know it isn't. I just like Sony phones. And Xperia SP seems like a good midrange option though it is more expensive than it should me atm.
The additional battery is indeed a good option for those who own a S3 and don't have money for complete replacement of the phone. S4 is indeed a marvel in all aspects. Comparing it to other phones is not fair atm.
Xperia SP would have been a fantastic phone but the 8GB(5GB usable) internal memory ruins the package. Pretty much all mid range android phones seem to get it horribly wrong as if someone buying a mid range phone wont be interested in playing alot of games. Its not like something like the SP is not capable of high end gaming because it most certainly is.
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Anyways to the OP One X has better screen and better feel in the hand. S3 has it beat or matches it in pretty much everything else you can think of.
As far as the "look" of the device is concerned that is purely subjective. S3 is available in a variety of colors and some of them really do look good. Secondly S3 is just such a popular phone that it almost doesnt matter how it looks, everyone knows what phone it is and everyone knows its an expensive phone. I am talking about the "showing off" aspect of looks otherwise ofcourse it does matter how a phone looks for personal satisfaction.