Amber on android is the best solution for android, as the signer is always local.

Nak is my goto but only cli based so out of scope for most people.

Gossip is really good too and I use it extensively.

@BlackCoffee is working on a hardware device, like a coldcard for your nsec that does remote signing.

Nip-46 is still rough around the edges, mainly because the spec was so bad at first and there were so many iterations. It’ll be better. 

 That said, I think there is a lot to be said about large clients becoming signers, @jb55 expressed interest in doing this at some point, so did @miljan