+Pihole is free and open. It is also yours to build,manage,customize as you please.
-NextDNS is also further away, meaning there will be much more latency for all your DNS queries. It is usually best to run your own resolver, or have a local DNS server in your network.
+Pihole sits on a device on your network. You can also enable recursion directly on the pihole by installing Unbound on the same device.
But your local PI resolver would likely have to pass on your request to an upstream DNS server if it isn't cached. Although its negligible, this extra hop would add latency. This is assuming the result isn't in the OS or browser DNS cache.
There are tons of important details to keeping a critical service up and running almost all the time - even if you are competent in this, that is still time every month making sure it's running, secure and functional.
The only reasons in my opinion to DIY a solution would be a) learning, hobby or for fun or b) you have requirements that can't be met another way, like privacy goals.