which one is best? What are pros and cons for each one?
A fret board with some relief should give a better action over more of the frets. A flat fret board should be quicker to make and repair and give good results for action over the most used parts. Since relief only needs to be a very small amount it can be hard to be sure what is truly flat. A neck that is built flat may well develop a slight amount of relief when the strings are put on. The subject does ignore another factor, that is the compliance or flex of the top. I am told that a guitar with a more compliant top "feels" easier to play under the left hand, and that is the ultimate aim of the luthier.
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