There's no denying that using a custom DNS server is a better choice than sticking with the one provided by your ISP, but the catch is that you shouldn't opt for the first DNS provider you find positive reviews of online, or the one everyone recommends on Reddit. There's a way to test which DNS server works best for you that only takes about a minute of your time, and it'll give you better results than blindly choosing from the most popular options.
The best DNS for others might not be the best one for you
Your location and ISP play a major role
To find out which DNS resolver works best for you, you should use a DNS benchmark. Most DNS benchmarks focus on latency and give you a list of the DNS servers that respond fastest for your location and ISP. You'd think location would be the only deciding factor, since the DNS provider with a node closest to you should be the fastest. In reality, your ISP matters too.
Even if you don't use its DNS server, your ISP still picks the route your DNS queries take. It may send them along a longer path that skips a certain provider's local node, so a different DNS server ends up being faster for you, even though the first provider has a server closer to your location.
This also means what works for you won't necessarily work for your neighbor if they use a different ISP. That's why you should run the test on your home network. Conversely, if you want the best DNS server for your phone and you're mostly on mobile data, run the test on mobile data rather than Wi-Fi. Lastly, if you keep a VPN on all the time, run the test with it enabled, but if you only use one occasionally, turn it off first.
Here's how to test custom DNS providers and find the one that works best for your network
All it takes is a single click and a minute or so of your time
Now, there are plenty of DNS benchmark sites out there, but I'll focus on two today: DNS Speed Test and DNS Speed Test by DNS provider Control D. The first one is simpler and only focuses on latency, giving you a list of the fastest DNS servers for your home network. In my case, Cloudflare was the fastest, which happens to be the one I use on my desktop PC. But this doesn't mean other DNS providers aren't fast enough. For instance, the difference between first and 10th place was only 20ms, which you'll hardly notice when opening pages.
DNS Speed Test by Control D is more detailed. It doesn't just measure latency; it also tests for jitter (how much latency varies between queries), availability (the percentage of queries that complete before timing out), median cached and uncached resolve times (the cached p50 and uncached p50 numbers in the results), and worst-case resolve times (the p95 number in the results). Once again, Cloudflare was on top, but the others weren't that far behind.
Control D's speed test only tested seven DNS providers in my case, so if the one you'd like to test isn't on the list, you can add it by clicking the Add custom DoH resolver button and entering its URL. You can also see that the test includes different categories: General, Gaming, Streaming, and Power User. These weigh the measurements differently: General balances median latency, worst-case latency, and jitter, with a bit of weight on availability; Gaming prioritizes consistency (jitter and worst-case latency); Streaming favors median latency and availability; and Power User weighs all metrics equally.
Finally, note that Control D's speed test only tests DNS servers that support DoH (DNS over HTTPS). Since my ISP's DNS server doesn't, it wasn't benchmarked, as you can see in the screenshots. So if your ISP's DNS server supports DNS over HTTPS, you might be able to test it here, too.
There's nothing stopping you from using any DNS you want
Just don't pick one that bombed the benchmark
Once you get the results, you don't have to blindly stick to the DNS provider that scored the best. Remember, the differences are measured in milliseconds. Even if some other provider is, for example, 10ms slower than the fastest one, there's nothing stopping you from using it if you prefer its features or just like it more than the others.
Just make sure the provider you choose doesn't bomb the test with extreme slowdowns or low availability. As long as it's fairly quick and reliable at resolving DNS queries, you're golden. In my case, Cloudflare, the custom DNS server I'm using, happened to be the fastest, but I'd be fine with any of the top 20 providers in DNS Speed Test's benchmark, or with any of the providers tested by Control D's tool.
At the end of the day, speed isn't the only deciding factor. Some DNS providers can also block ads (AdGuard, for instance) or malicious websites and adult content (Cloudflare's 1.1.1.3 resolver), while others provide a bunch of custom controls that let you fine-tune exactly what gets blocked and allowed (NextDNS). These features can be more important than simply being the fastest.
Whichever DNS you pick, it likely beats sticking with your ISP's
Whichever custom DNS provider you end up with, it will be a better choice than your ISP's default DNS resolver, as long as it ranks relatively high in your benchmark results. Not only will your queries be more secure, but there's also a good chance a custom DNS will be faster, with many custom providers also letting you block ads, malicious websites, and more.