That is the non-objective part. I have to start somewhere. I have a list of 1352 relays that my gossip client has encountered over the last 15 months. This is based on my personal usage. These particular relays, and especially their ordering (scores) are very much based on my personal usage... they might be very different for someone else's nostr experience. But I don't have a better place to start. At least the ordering is coorelated with popularity and success.

A better starting point might be to get data from stats.nostr.band or something, which has 2231 relays and can rank them based on users per relay or events per relay.