"Best" sound depends on the location of the mics, mics used, the audio level produced by the subject and the ability of the recording device to control the audio level being recorded. Your question is simple, but these often have the most complex answers.
What is your budget? Camcorders range in price from $50 to $50,000. The capabilities vary greatly between them. Once this is established, we may have a pre-defined "short list".
What is the planned proximity of the camcorder to the performer(s)? Even acoustic music can be too loud or too soft for many camcorders' built-in mics to deal with well if the camcorder (hence the built-in mics) is not in the "right" place. To get around this, external mics (or an external audio recording device), can be used.
Ideally, a camcorder with enough flexibility is appropriate. This would include an audio-in connection for external mics and manual audio gain control. The Canon HF S series, HV40 and Sony CX500 series and HDR-HC9 have an audio-in connection for external mics and decent, granular, manual audio control.
Alternatively, ANY camcorder can be used - along with a properly placed "audio field recorder". The audio captured by the field recorder can be sync'd with the video during editing. Then mute the audio captured by the camcorder...
The question of what you want to do with the video/audio after it is captured to the camcorder begs to be asked...
I want to buy a camcorder for my son's recital. He is playing violin and in a music school. I am looking for a the best sound capture camcorder. Any idea?

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