There isn't a huge difference in performance between the 13" and the 12" anymore. To me, its about more then power, its about screen real estate. The extra space is a boon if your serious about multitasking.
Your free to disagree with me, and thanks so much for letting me know lol.
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I mean, it really has nothing to do with your size. Big and small people a like like the 15"

And I agree, they are completely different machines... but we are talking about less then two inches. The 15" is 13.75 inches wide, and the 13" is 12 inches wide. If it makes that big of a difference to you I'd say go with the 12" MacBook.
Since we are going to talk about our feelings, I do feel like the 13" is a joke. It's a fine machine, but its just skimpy. I feel like those that "love" the 13" just can't afford the 15" or don't want to spend that much on a computer, and they are just trying to make themselves feel better. And that is fine. Even if you discount the the fact the 15" has a quad core i7, 16 GB of standard memory, a GPU that is insanely more powerful then what the 13" offers, your still left with one huge, glaring difference: the screen. And what a huge difference it is.