I say stay away from all three of them.
But over the last 5-6 years, I can't recall too many Gateway computers that have been decent, I've heard hardly any praises for gateway from people I know, nor computers I have personally been on. While I've actually heard people praise Dell computers. Though dell hasn't been out front the gate and leading as much as Gateway did over those years. But that's just a marketing thing there as to why Gateway had the that lead.
as far as lap tops/notebooks go, that's a different case. This is the place Dell takes a dive from experiance, but then again...all those laptops that had problems from Dell were running ME, so I can't really place that all in Dell's lap. Because any system running ME is high risk for many complications.
Anyone would be much better getting a pre-built computer from a smaller known company, know people that have had good experiance with google.com assembled computers. Go to sites that are known but also small production where you can select each component. Or better yet, build the computer yourself. Or at least get a bare-bones unit so the more difficult components will already be assembled. And you can hand pick the very easy installation components and get great deals for great quality.
Motherboard/heatsink installations is the most difficult part about building a computer. Everything else is pie.
another thing about the Dell, Gateway, etc. they sometimes (pretty much all production lines from dell/gateway these days) in their computer put only a limited bios, and OS install. And while most people can do just fine and dandy like that. Wanting a serious and fully operational home development PC (audio recording, video editing). Often you'll end up in there, at least once to disable or enable something. And if it's not there to even fiddle with, have patients and hope customer service is in fact there.