I bought a AW5790 prior to them getting discontinued a few months ago. It is by far the best peice of equipment I've ever owned.
Alienware was "Dell" at the time, but let me tell you, thats just stock wise. The professionalism they have is astounding in todays PC world. I loved every second of even ordering, and they guy on the phone didnt even try to force upgrades down my throat. I had a $1400 budget, and he helped me get it to 1398 AFTER shipping.
Plus, their KB and support line will actually help you replace components. IE, they have complete picture tutorials for replacing RAM, Video Cards, CPUs, HDs and all in YOUR laptop. Not a generic one, but literally your model number. And with AW you get all components that were DESIGNED to be removed/upgraded and placed in great spots. Vents are in good spots, power cords, USB plugs, volume, ability to easily turn off touchpads, etc etc etc.
Every time I call their support lines, I get a quick answer, always informed person who will tell me pretty much anything. Last time I called was to get MAX RAM for my model(since AW had 2 versions of my 5790, I wasnt sure the max, one was 2gb and the other was 4gb). He looked it up in about 10 seconds and told me, plus he let me know about the KB artcile and option to call support for help while changing them out. Didnt try to force AW's own RAM upgrades on me.
The laptop is a very sturdy machine. Not "Plasticy" by any means. I've nver been on a MBP, so I cannot compare the diffs.
When I got the machine, it had nothing but my OS installed, and a text document with every serial number, model number, several benchmark results, and contact information in it on my desktop. No Bloatware.
For your usage however... I'm not sure I'd use a AW or XPS. Heck, even a MBP seems like overkill. I'd think you'd be more interested in extended battery life and lightweight than a heavy power hungry beast.
Anyway.. just felt like I'd give my perspective on AW. I love them for notebooks. Still think desktops are to be selfmade, but for notebooks, I hope I can always afford to buy from them.
It is by far the best company I've had the pleasure to buy from. Their Quality and Performance can't be beat.
[edit] Don't forget that I said I'm not comparing! Just giving my experience with AW.