Honestly, if you're just gonna be using the computer for nothing besides watching movies/shows, writing papers, listening to music, email and internet, and stuff like that, the Macbook or any other computer is probably fine.
On the other hand, I don't know anything about alienware, but I've had the basemodel Macbook Pro for about a year, and honestly, I'm not that impressed. I've been doing a lot of design work (adobe, autocad, sketchup, etc) and it lags like a mothafucka when I've got photoshop, indesign, and illustrator going (it literally says it ran out of memory multiple times). In hind sight, I would've gone with the next step up, but a memory upgrade might solve my problems, though the upgraded graphics card in the other models might really help me out.
All in all: I like the mac because the os is so much more intuitive and user-friendly. I'm not totally against windows, especially as it's vastly improved lately, but osx is so much easier to use in my opinion. Also, the hardware is built for the software; the trackpad makes shit soo easy with different tasks with multi-finger swipes and the clickable trackpad is sick once i got the hang of it. Also, expose and spaces rocks my world. It just works as you'd expect it to.
I'd recommend the mac depending on what sort of use you're expecting to use it for--it's really not worth it to spend the extra 400 bucks for the aluminum case if you don't need the minuscule upgrade in performance.
Also, I have an android phone and getting music on it from itunes is a breeze, if that's a concern. Also also, everything works seemlessly using a flash drive between mac and windows as far as I've seen.
