I'd buy the computer when u need it. If u need it for school, I'd get it the week b4 u go, that way, if theere is an update, u will get it. Which system u get depends on your budget; get as much as u can afford. I have the MBP, but it is pricy compared to the macbook. The low end mbp is about the same cost as the MBA, but is much more powerful and functional.
I have the matte screen and love it. That is totally personal preference.