Asus, but your not getting a gaming laptop for that much, i know of a netbook that will play GTA 4 for under your budget if you want to know it. but AlienWare is over priced, your paying for a brand (like a Mac but you still get windows).
You probably won't find a great gaming laptop around $600.
However if you have hope, Dell/Alienware have great laptops and desktops made exactly for gaming.
Again, $600 may not give you much.