Well let’s clear something up straight away.
With the exception of including the word “Pro” in the name, the Surface Pro is in no way comparable to an MBP, and isn’t supposed to be. That includes price.
There are much better pieces of kit available on the Windows 8 platform that are indeed comparable to the MBP (or the MBA) for similar cash.
Firstly, you are considering two very different operating systems so your first decision should not be about hardware, but more importantly:
Mac OS X or Windows 8?
If you’ve not used Mac OS, try it in an Apple Store for a period of time. It has a lot (really an awful lot) to commend it, but some people (myself included) simply don’t get on with it. The same is true of Windows 8, of course, although I do find I quite like the system now.
After that you can consider questions of portability, screen size and resolution, memory, hard drive, processing power and of course price that will bring you to an ultimate decision.
I’m not sure movies would be any better viewed on a Retina screen (anything more than full HD would be wasted for all but a few Super HD movies available on Netfilx, I think?). But for that sort of use, a screen is clearly important. Sony’s latest line of Win8 machines basically have Bravia TVs as monitors, so are amongst the very best you can find for deep blacks, rich colours that cover the entire RGB gamut, and wide viewing angles. The Sony Pro is a fantastic, light ultraportable and worth a look if you prefer Win8 to MacOS.
As for screen size: my personal preference would be a 13" anything. They tend not to be noticeably heavier, have better ports, and have more screen space. Remember portability really means two things: weight and thickness. Those are the only two measures that will make a real difference in any bag / briefcase / rucksack appropriate for carrying a laptop.