relay reliability and performance is so volatile in nostr, the simplest way is to simply broadcast to 100 relays, probably 30 accepts your event

although it works this way best from command line, as uis may slow down if too many relays are configured

imo two main metrics are:

- does the relay accept your event

- is the event retrievable

one thing to note is, that sometimes relays say they accepted the event, but the event cannot be found when queried.

events do not propagate by design. event propagation from relay to relay is undocumented feature.