I heard gateway has a crappy tech support in the sense they are not as open as Dell is in exchanging or replacing parts. So i would go with dell. They ahve great tech support. in fact, my friend called them once at around 3 am PST and there was someone there at dell headquarters to help us.
In addition, my friend, who bought a computer with them in 1998, has had his monitor replaced 3 times at no extra charge.