1: What features you want to see in a wallet which is not in other ones
Though BlueWallet fortunately now has their own privacy feature(Payjoin)[1], I'd want a wallet with a coinjoining feature like how Wasabi Wallet does it.
Besides that? I couldn't think of much to be honest, as BlueWallet is a pretty good wallet in my opinion that has my needs.
[1]
https://bluewallet.io/features/[2]
https://wasabiwallet.io/