These are the most spam-filled relays:

wss://nostr-relay.digitalmob.ro

wss://nostr.drss.io

wss://nostr.einundzwanzig.space

wss://nostr.swiss-enigma.ch

wss://relay.nostr.bg

I've removed them from NostrGram's indexing because they have (literally) 100x more spam than other relays.