I've had a few Alienwares in my day, mostly when I was younger. Since then I've switched to using mainly Asus and MSI machines for most of what I do, and in all honesty I prefer my MSI to my fabled Alienware 17.
The gaming laptops I have currently are the Alienware 17, the MSI GE Series GE60 Apache Pro-867, and the MSI GT80 Titan SLI.
The Titan is its own breed, but between the first two- the alienware and the MSI GE- I prefer the MSI.
Since Alienware worked their way under the Dell umbrella, the customer support is total ass (I believe that is the technical term) and the components are more and more breakable, like, better keep that thing on its own table. I was thinking about getting the new Area 51 tower, but was quickly dissuaded by peers and coworkers who'd had experience with Dell.
So I'd definitely recommend MSI or Asus over Alienware.
However, if price is an issue, it is hard to get a good MSI for under a grand, as others have said. Asus makes some good gaming laptops for a tighter budget, in my experience.