When connecting the laptop to larger screen TV's, your laptop has to have a decent video card. So that needs to be taken into account.
It depends on how much your carrying it around and your desk/work space. I have 2 laptops. a 17" and at 14.1". The 17" is a pain in the ass at work because I have to lug it all over the place and set it up in tight work spaces. It's noticeably heavier. However, the 17" is much better for movies. IMO, the desk space that the laptop takes up once it's set up is a greater factor than the weight. So as long as your work areas aren't to cramped and you're watching a lot of videos then I'd get the 17.