Have you checked out Jumble.social yet?

It's a great web client to use, especially when trying to decide what relays you want to add. You can see which relays those you follow have favorited, you can build relay sets that give you a feed of all content from those relays, or you can just look at what is being posted to a single relay.

The most popular relays that a large percentage of Nostr is using would probably be:

relay.damus.io

relay.primal.net

nos.lol

And if you add relay.nostr.band, which aggregates notes from a large number of other relays, you'll probably have a pretty broad view of Nostr content.

You'll also have a lot of spam. 😂