I have a Robot. It's the most durable, can be programmed and can be switched off if required.
Also, being a robot it would never physically or mentally tire, so I could just send it to work the most monotonous, physically demanding yet highly paid job while I sit at home.
A Clone would be awkward, especially with things like Human Rights and Identity Theft.
A Doppelgänger would be downright creepy. Traditionally Doppelgängers are portents of impeding doom and are considered evil or malicious in most Folklore.