The answer is the same as the answer to the questions, "What is the 'best' exposure?," and, "What is the 'best' composition?" Simple. It's the one that you like for the shot in question.


It is worth pointing out that like white balance, if you shoot RAW you can select whatever picture style you want in DPP with no penalty (and conversely, if you shoot JPG, changing picture style degrades the image). So, shoot RAW and fiddle in post, if you're so inclined. Also note that only DPP can use the Canon picture styles (including the extra ones available for download, like Autumn Hues and Twilight). Other software package do have similar options, though.