Last updated May 27, 2018
Part 1: Wifi Versus Wired
The Short Story
Plug In! (And disable wifi) The Long Story
No matter how great your wifi is, or you think your wifi is, you are always better off wired. Period. The reason why boils down to interference and packet loss. A wired connection has a shielded cable that all but eliminates any local radio interference. A wifi connection, no matter how modern and how close you are to your router, will always be prone to interference. If you live in a city, even your neighbor using their microwave oven could interfere with your wifi signal! Nevermind all of the electronic gadgetry that we use all around us every day ourselves in our own homes. If you have the option, and even if it means buying a 50' cable and running it up the stairs from your basement to plug in, do it! (You don't want to be the guy that everyone dreads playing because you have a spotty connection.) Another option, mentioned by Smozoma below, is Powerline Adapters, which use your existing power outlets and wires to create a wired connection, all for less than $100.
People sometimes convince themselves that wifi is "good enough" because they see their ping rate, and it looks good. Heck, if you can stream Netflix in HD how the heck can't you play this ancient videogame. Why not? Because it is not the same thing. At all. Among many difference, video streams like Netflix get buffered, so there is a lot of "wiggle room" to make sure you get what appears to be a smooth feed. In online games, there is no wiggle room. You want your button presses to register NOW! This is all about ping and latency (which can be disrupted by radio interference), and has nothing to do with bandwidth. When you do a ping test with wifi, you might see your connection is great, and it is: At that very moment, with no interference. But then, at seemingly random times, you will get lag spikes, even though things started off great. These are not really random. They are the microwaves, baby monitors, various electronics and even other people's wifi, interfering and grinding your games to a halt.
Ethernet Versus USB Versus WiFi
For our purposes, any wired connection -- whether Ethernet or USB (via an Ethernet to USB adapter) -- beats WiFi. Again, because of the interference. Nowadays there seems to be a trend to design laptops with fast USB ports but no Ethernet port. If you are in this situation, do not be tempted to use your laptop's built in WiFi, or to plug in a USB WiFi adapter. Use a USB Ethernet adapter to get that shielded cable plugged directly from your router to your computer, staving off any possible radio interference.
Part 2: Overcoming Great Distances
The Short Story
You can't overcome great distances. The Long Story:
If someone in North America plays someone in Europe, you will feel it. There is simply no way to overcome the great distance. While light travels in a vacuum superfast, electricity through (copper) wires is much slower. It is slower in absolute terms, but it is also slower because wires zigzag, and repeaters, switches and routers all conspire to grind things down significantly, as well.
Because you cannot defeat the physical reality that long distances will slow things down, you need to do everything within your power to help a tough situation. Here is a thread worth reading: Overseas Games and Laggy Connections.
Part 3: Cable versus DSL versus Fiber
The Short Story
People are successful with any of them. A Note on DSL
For the lowest possible Ping rate, it is a good idea to have your ISP "disable interleaving". In a nutshell, "interleaving" is some extra error correction, which will add a small bit of time to your ping rate. This correction is probably helpful for streaming videos, but a real annoyance for playing NHL94, where we want our button clicks to register *now*! You can read more about it here: https://www.gpforums.co.nz/threads/292343-Interleaving-Explained
Unfortunately, you will have to have your ISP turn it off for you; you cannot do it yourself.
...More to come
- tips on how to have better connectivity
- minimum speed requirements (anything faster than dialup usually good enough)
- hamachi vs client server connection
- anything else any networking peeps can think of?