From an email: Common question about temperament
"I play ... blues, simple jazz, little country. I play single tone, multitone, chords, arpeggios (triades, 6th; 7th), different modes (or positions). Tongue blocks, splits,
What kind of tuning is optimal for my style of playing?"
Since you play single, multiple, chords and arpeggios but you also play in different positions, the answer is not straightforward. But the problem may not be too big, either...
If you have played both stock Golden Melodies and Stock Marine Band or Special 20s, you have experienced both temperaments. And if you don't have a strong preference at this point, then either temperament should work for you - the question is which do you prefer? How important is it to you? Is this really a big problem?
If we focus on the reeds that are tuned as major thirds, that's the most noticeable difference. So holes 2, 5, 8 blow and 3, 7 draw are tuned about 12 cents flat on Marine Band type harmonicas. When playing in positions/modes/scales where those holes are the tonic or the fifth, I feel like that's where it's the most noticeable. The single note is flat and if that's your tonic, the whole scale may seem unstable. Or for example, the major scale in third position - the second and the sixth note on the bottom octave feel a little off. They would feel better in equal temperament.
But if you tune those notes to be equal, the major triads and even the splits can offer less power, less harmonics. One of the features of a custom harmonica is the precise tuning which provides powerful harmonics if you tune for harmony. The sound from the major triads in harmony can fill the room (as Joe Filisko says, little instrument, big sound!)
I am sorry but you can't have both! Not on the same instrument at the same time, anyway. So the choice is a matter for you to decide. But I hope I have given you the information to make that decision. Please let me know if you need me to elaborate further.