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)