Signal seems the easiest and most intuitve to onboard close people I know to, even then they're still reluctant to break away from their default messaging apps.
I like simplex, but mainly to send to myself over multiple devices without needing a phone number linked for an account, would also gladly use that if I could convince anyone I know to use it.
Also rooting for things like White Noise, just have even less of a reason to use it as I'm rarely in group chats or DM anyone on nostr, and for the normie acquiatance that has next to no knowledge or understanding of nostr it's still too much despite how clean it is.