Valve games aren't demanding, so you can get by with either.
I'm wondering, how do you guys take care of the OS? Seems like all the discs are single license nowadays, and when I built my second rig for my mom, I had to resort to bypassing activation, which neither of us were comfortable with. Do you usually ask friends to use their windows OS? Cus that is where the large distributors have the upper hand. They get the licenses for dirt cheap it seems.
If you want to play more recent games though, you should definitely get better graphics cards than the ones in the listed prebuilts. The gts 250 has been rebadged beyond reason, it's on pretty old architecture, while the ATI there is on their lower end, worse than the 250 I think.
http://www.newegg.com/Product/Produc...2E16883227179R
consider this one. It has an hd 5770, which is a step up from the gts 250 even when you exclude the dx11 capabilities.
Larger power supply, nicer case, better processor.
Only downside is it's an open box item. Should be pretty safe though, right?