these are two totally different classes of notebooks, though they are specced very similarly.
the vaio is a great computer, especially because its 13" but its priced way too high for me. if the machine had core i7, 1920x1080p screen, and blu-ray as standard, it would be a great deal, but it doesnt. i know there is minimal difference between the i5 and i7, but the screen alone is worth the investment, and it would be kind of silly to see a high end sony notebook WITHOUT blu-ray (imo).
on the other hand, the mbp 15" will give you a physically larger screen, but inferior resolution (1440x900, unless you spring for the 1680x1050 glossy or matte upgrade). also, the mbp comes with either 320GB or 500GB hdd, but the vaio comes with a 128GB ssd. however, i personally prefer osx over windows, and having the ability to run both natively is just awesome. not to mention, apples service and support is the best in the industry. being able to go into any retail store and drop off your computer for repair is great, as well as being able to get ahold of american based tech support on the phone if needed.
for me, i would say go for the mbp 15" with the 1680x1050 matte/antiglare screen.