For the love of gosh please do not get an Alienware or a Macbook.
I know that there are people who will continually say "blah blah I can game on my Mac" or "derr hurper Macs DO work for gaming." These statements might be true, but why pay more for something when you could pay less for more benefits? Plus, there are way more games that work on Windows than on Mac. There is just no logical reason to get a Mac unless you're a fanboy.
As for Alienware, they make good computers, but they are way too overpriced. Alienware and Dell are just your average consumerist big businesses that make their PCs appeal to the average person with a bunch of bells and whistles. They aren't bad; just overpriced.
And Chromebooks are just out of the question. They are just not made for playing games. Period.
My suggestion? Get a desktop. Either build it yourself or get one from Tigerdirect or something.