I think it depends on your current situation. If you just need to get some code written, hire B, assuming you can cope with getting B up to scratch to write said code. If you're earlier stage -- you need to brainstorm, to have those tangents, that little spark of something-else -- hire A. Give her 20% of her time her own, and watch magic happen.
Disclaimer: I'm totally an A (although probably with more randomness and less skill), so I might be biased.
Disclaimer: I'm totally an A (although probably with more randomness and less skill), so I might be biased.