A few of my thoughts on concert pitch – modern concert orchestras currently tune to A=440, A=442 and A=443. Soloists with orchestras often tune slightly higher than the orchestra they are playing with, to enable them to stand out.
An orchestra has an advantage in recording slightly higher than its competitors. When auditioning tracks, side by side in iTunes, the higher track sounds more brilliant and impressive.
Harmonicas are often tuned slightly higher than A=440, because in performance, notes often become flatter when played loudly. Same principe with melodicas.
There’s also the question of wether you want to tune your melodica to ‘equal temperament’ (equally spaced intervals, like a piano), or ‘just intonation’ (a more natural, consonant sound). Of course, with ‘just intonation’ you’re limited to specific keys, but the pay off is a more harmonious sound. This is something I plan to experiment with…
But at the end of the day, it’s whatever you’re happy with to suit your playing style, and the sound you want to achieve. Nothing quite beats the feeling of turning up to a music session with a freshly tuned melodica!