He would use all the tools that make it possible or easier to write good software (version control, tests, continuous integration, possibly code quality metric tools) without being married to one in particular. He'd switch to better languages and tools as he becomes aware of them, as far as the switches are practical.
He would have a broad overview of the underlying theories (algorithms, computability, complexity, various fields of math), and dive deep into those that matter for the problem at hand.
He'd write clear documentation that the end user can understand.
He'd continue to evolve his tools and skills, and where he finds the current tools lacking, he'd improve on them, or even write his own - but only so far as it doesn't distract him too much from actually producing the software that is his focus.
He'd be aware of his customer's requirements, and equally important, of the goals behind those requirements.
He would be aware of security and moral implications of his software, and refuse to compromise on them.
He wouldn't rant on hackernews, but be available for mentoring to those who strive to imitate him.