Fighting games are peer to peer connections. Paying for better internet or having a 'better connection' isn't a real thing here because the only thing that matters is your direct connection with your opponent. You can't magically send him packets faster than they can send you packets. You have zero control over packet loss once the information leaves your home, just like they have zero control over this issue. The only thing you can do here is just avoid using Wifi... but if your opponent is using WiFi, packets will be lost and it will effect you both.
There really is no such thing as being 'the person with the good connection' in these p2p cases outside of the above. Its just a matter of distance(time) and loss. Thats it. Paying for "faster" internet just gives you access to a fatter pipe. You can send and receive more data at once. But these games use very little data per second, and you don't need a fat pipe to play them nicely. And no amount of upgrades will actually make the data travel faster across the world.
While this is generally true, I'm going to tack on an addendum here for troubleshooting some problems that can exist and be solved at home:
Bad wiring at home can cause signal loss and related issues. At my previous residence, the cable connection came into the house on the bottom floor and had to be wired upstairs through several cables and a few splitters before it connected to the modem. This induced a ton of packet loss and generally poor performance across the board, and I had to get a local Comcast tech to boost the signal to fix it. I can imagine similar problems being caused by powerline adapters with less than stellar electrical wiring, too.
There are some articles out there that explain how to check your modem's status page and what you should be looking for there to diagnose poor signal levels:
The tl;dr is that downstream PL should not be too far above or below 0, downstream signal-to-noise should be 35+ (the higher the better), and upstream PL should probably be 40 to 45 but can vary a bit from that depending on specifics. If any of those numbers are way off then it's indicative of a problem between your modem and the local ISP and you should probably call a technician to fix it.
And even though bandwidth doesn't matter for gaming, doing a simple speedtest can still be useful in some cases. If you're paying for a 100down/20up connection, for example, but are only getting half of that in practice, then it's a sign that you're either being throttled or suffering some major signal loss somewhere.
A traceroute command to a few random websites (ex: open up Windows command prompt and type "tracert google.com") can also help pinpoint where in a connection chain that the latency spikes the most. If you're tracing a connection to a server on the other side of the planet, but your latency jumps up by 50ms or more before it even leaves your city, then that's a problem close to home.
