DNS0 vs NextDNS

dns0 seems perfect for a no nonsense hardened nextdns setup. You can't customize anything other than zero or kids but you can be sure that almost everything will work without any setup.

Think of them as complementary rather than competing services. dns0 is based in the EU, there are never any logs, and it's completely free so that's a plus but other than that it's very similar to nextdns. 

I'd recommend dns0 for corporate environments or people who will only do general browsing as that's what it's best suited for. Use nextdns if you really want to customize your browsing experience making specific block or allow lists, filters, security settings, etc. Basically customizable dns0 which is what it is. I'd say nextdns is also better for adblocking if that's what you want.