Xbox One downloads
uTorrent
Blizzard downloader
Steam downloads
XB1 is the worst, it will kill everything and make it hard to load simple web pages. uTorrent varies from the same, to barely noticeable. Blizzard downloader and Steam downloading will make it noticeable for Netflix or gaming, but web browsing is mostly ok. PS3, Wii, Wii U, and Xbox 360 don't do anything noticeable, nether does Netflix (regardless of device used). All problem devices/programs are connected through wired to the same router. We've actually tried 2 routers, with the same results.
Linksys WRT54G
Linksys WRT54GX2
Our internet connection is DSL, fiber up to the house (but we don't pay for fiber speeds). We get the exact speed we're paying for:
Since we're experiencing the same thing with other devices it may not matter, but I've got the following ports always forwarded to my Xbox One (in order for it to show my NAT as open):
Port 88 (UDP)
Port 3074 (UDP and TCP)
Port 53 (UDP and TCP)
Port 80 (TCP)
Port 500 (UDP)
UDP Port 3544 (UDP)
UDP Port 4500 (UDP)
OK so the obvious answer would be that anything using all of our bandwidth will clog the network. What I don't understand is why some applications/devices do it more than others. Why can we have 3 Netflix streams going and maybe see a little loss in quality on them, but browsing is fine? Then I start a 400MB download on my Xbox One and you can't connect to anything until it's done. I'd blame the router, but we've tried 2 different ones. (though both are older routers of the same brand. Maybe Linksys routers from that era have issues?)