Not a lot of difference between the two brands.
I've owned both over the years. I still have two dells in the house. One is my wife's computer, the other is my wife's OLD computer...handed down to the grandkids.
BOTH companies tend to use the cheapest components they can get. Motherboards and other things are specially made for them, often by Foxconn, and are cheaper in price and quality than the retail products that we have to choose from when building our computers.
Video cards are a mix of OEM builds and the same models as we buy at retail...but are usually custom-made for Dell/Gateway to their specifications.
Processors are usually the same as we can buy, just the OEM packaging.
I've seen your other threads, but don't remember the specifics. (hey, I'm old)
What is the primary purpose of your computer?
Dell and Gateway are both fine for someone who doesn't want to tinker with their computer, wants a general-purpose computer rather than a high-end dedicated gaming rig.
If your main use will be things like web surfing, office-type applications, and light gaming, you'll be fine with either one. (I prefer Dell, but Gateway isn't bad either)
If you want a machine that will run the latest games with all the eye-candy settings maxed out, you're either going to have to spend big bucks on one of their "custom gaming machines," find a different brand, such as IBuyPower or Cyberpower, (Alienware is now a Dell brand) or one of the other high-end gaming rigs, OR, take the plunge and build your own.