DarkSend is here now (albeit currently in beta), it works, it's built directly into the client.

Dark Wallet is currently vapouware, will require browser extensions and other layers of code, providing a far bigger attack surface. And it's still tied to BTC, (though I suppose it could be modded to work with any coin) and BTC has other problems, godawful transaction times for a start, and a core dev team that is just too slow and indecisive these days. Plus the level of centralisation in the BTC network is just scary, and is getting worse.