I would buy the 1366 by 768 res screen because for me FPS is the most important element of gaming and with this video https://www.youtube.com/watch?v=QdyiRn1r2r8 alienware shows us that its tiny core i5 & 860m simply do not deliver.
That's why I got the i7-5500u instead. While it's not the most powerful CPU out there, I think it'll make an appreciable difference in framerate.
The 720p screen is a 200 nit TN. I got the 1080p screen instead, becuase I'd rather have the 1080p IPS with 350 nits than a 200 nit TN display.