They are different things. Try both, see which you like better. Nostr is a protocol which means many apps can interoperate together.
Discussion
isn’t bluesky built on a similar protocol, AT? how is nostr different from AT
I don’t know much about AT protocol. I don’t believe they are similar though.
AT is client/repo/indexer. The data lives on a “personal” server. But unfortunately it's all on one company server right now. The idea is you could host your own repo (with a traditional hosting provider, on your own server, or clone a GitHub) and if a indexer blocks you, a client could still p2p someone to your repo. There are some very early client's (mostly Japanese), but with out a way to sign from extension, it's not safe to test them with your main bs account, I'm told they are internally working on a signing extension. IMO: They are very concerned with moderation, and want to protect the brand of their client before opening up the protocol. But, if developers from the outside dont build out a vibrant competitive ecosystem, it currently is, and will remain just moving the bird from one cage to another.
Nostr is client/relay based. The data lives on multiple relays and is pulled down to client's via open websockets. the idea is if a relay blocks you, you can still be found on other relays, or worst case spin one up yourself. we already have signing extensions, and remote delegation, so moving around playing with multiple client's that offer different experiences from a diversity of developers not under one corpo roof is very much a reality here.
nostr, as others have mention, is also Notes and “Other Stuff” Transmited on Relays, social media is just one use case.