In short, it’s mostly word of mouth and trial and error. More relays are good for a robust network, but they are very hard on mobile battery life, data usage, and in my experience performance. I think many clients get hung up when one relay is slow.

There may be some tools that help document relay statistics, but I can’t say I’ve found many that give me a very reliable picture yet.

Most clients allow you to look at other users relays and my understanding has come from following relay devs and occasionally testing a new relay. For example, right now the highest performance relay software is strfry and I mostly try to use relays running on that (I think all 3 I listed are). Two of the 3 relays I mentioned are also default relays for two of the most popular clients, which ensures better coverage.

As a paid alternative, the nostr.wine set of relays does a bunch of behind the scenes aggregating and rebroadcasting on their end before you get the data. It provides a great experience but obviously does have a monthly cost. There may also be a free trial now.

A few relay devs with following and I’m sure there are many others I’m missing: #[6]​ #[7]​ #[8]