if we're talking laptops don't get either of them.
I have an xps laptop and they are the worst series dell ever made and they don't learn from their mistakes with earlier models.
I have an m1710 xps. Dell admitted that the architecture of the inside was one big flaw , yet they barely changed anything for future models. The studio xps that came out 2 or 3 years later had the same overheating flaws due to bad structure inside (a friend of mine has one).
With Alienware you generally pay too much for what you get. They used to have superb quality but since the takeover by dell they've gone backwards.
I suggest you look into asus.
edit: yes reviews may sound amazing but don't forget that big companies as dell often offer some stuff under the table for magazines and stuff to give positive reviews. For my laptop too there were no negative reviews in the first couple of months the laptop was on the market. after a year or 2 years alot of negativity about this model started , everywhere on the internet people saying their laptops overheated in idle mode, fried graphic cards, motherboards , etc . Also the support from dell (and alienware) is pretty terrible. For my model they haven't released a single graphic card driver in the past 4 Years.