If you value portability, the M11x is nice it has around 5 hours battery life, and very portable (from what i've heard anyway). Asus laptops are a lot better if you are looking to get more bang for your buck though. I have a G51J and it's been awesome, not counting the glitchy BIOS I waited until now to fully patch It can play almost any game on high/very high, so it suits my needs.
have you seen the M11x is real life. while yes it has good battery life the dam thing is HUGE. its about as larger than regular 15" laptops. And its weighs alot. I was thinking of getting one before i saw it in real life and was DAM.
the Alienware laptops are more like an desktop replacement and if you are taking it anywhere you cant use it while on the bus or train and stuff.
Of Course That's Just My Opinion, I Could Be Wrong