I was using Quad9 for quite some time, but I had consistent problems with the DNS sometimes not working.

In my local network I switched to pihole with unbound as the resolver. Though this does require a bit more setup. I have unbound setup to serve expired records from the cache & prefetch comment queries, this helps with most of the delay.

On my phone I use dnsforge.de when I am not at home for example, and haven’t had any problems with unresponsive DNS so far.