It isn't, Alienware is a premium custom computer company but is not the best in that price range.
Velocity Micro is a better company and they tend to charge about the same. Falcon-North West is the absolute best custom PC designer, but you pay for it.
If you want to get more performance for your dollar, iBuyPower and CyberpowerPC build excellent computer for the money, thought their support is a bit more of a hassle.
If you want to do the ultimate smart thing, research how to build your own. Buy the parts yourself and take it carefully. Getting into computer building isn't that hard, though it takes awhile to master it, so you should be ready with in a week or so if you research pretty hard. If you are interested, look up guides on Youtube and ask questions on here. It really is the best way to get the most performance for your money.