Here is a very rough estimate at the top 25 nostr relays from the last 2 months (offline relays removed) sorted by read popularity:

wss://nos.lol
wss://relay.damus.io
wss://eden.nostr.land (paid, shutting down)
wss://nostr.wine (paid)
wss://relay.snort.social (paid)
wss://relay.nostr.band
wss://nostr.bitcoiner.social
wss://nostr-pub.wellorder.net
wss://relay.nostr.bg
wss://nostr.mom
wss://relay.orangepill.dev (paid)
wss://no.str.cr
wss://relay.nostr.com.au (paid)
wss://offchain.pub
wss://relay.plebstr.com
wss://nostr.fmt.wiz.biz
wss://nostr.rocks
wss://nostr.mutinywallet.com
wss://e.nos.lol
wss://purplepag.es (kind 0 and 10002 only)
wss://welcome.nostr.wine (gathers posts from new nostr users, read only)
wss://nostr-relay.nokotaro.com
wss://filter.nostr.wine (paid aggregator/broadcaster)
wss://relayable.org
wss://relay.mostr.pub (fediverse bridge)