All three are reputable places to buy. It's much easier to get the educational discount (if you qualify) online @ Apple than it is in SOME stores *cough Short Hills NJ cough*
Personally, if I did not qualify for the edu. discount, I would buy on Amazon, because there is usually (dep. on where you live) no sales tax. I crossed the border to buy my MBP in Delaware for the same reason (they have no sales tax state-wide

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No matter where you buy (please don't think I'm treating you condescendingly/like a noob by saying this), get the AppleCare. It is the most worthwhile investment you can make into the machine (aside from the machine itself!) and will most likely pay off in the future. As I mentioned earlier, they offered to replace my whole machine with a brand new MBP when the new one comes out (within the next couple of weeks, God willing) because of GPU problems.
In any case, good luck!