The WWW is full of pro and con about this question. Diversity is definitely a good thing. But it has side-effects. Over time (if you don't cache for longer period) all of the providers you are using are able to track and create a profile even if you ask them random. So you could stick to one of them anyway. But for relayability you want prob. more then one. At the end there are only a few smaller providers like your nextdns indicating not to log anything. You have to "trust" them (or not) like the big ones.