Accidentals in MIDI Import

It's not a notation issue but a music theory issue - the correct spelling depends on musical context, not on any sort of arbitrary notational conventions. It depends on the prevailing harmony (spelling the note to fit the current chord), the nature of the melodic line (chromatic tones in ascendng lines are typically spelled with sharps, descending lines with flats) and also some purely practical considerations for the players (avoid unnecessary Cb's, spelling a line that moves by step so it *looks* like it is moving by step, etc).

Getting it right in all cases, or even most cases, would require some pretty sophistated artificial intelligence and given that even music experts will disagree in some cases, it's really an impossibility.

But there are a few heuristics that could be worth employing. I think the smartest thing would be to go off the key signature and use a table that gives the most commn spelling off each note. There are only five notes to consider: the five notes of the chromatic scale that are not in the key. You'd use the the same basic table transposed for each key, except possibly modified by a user option to favor B over Cb and so forth.

Off the top of my head, and without going into detail into why (but I think any other theorists will recognize my reasoning), I think the table should probably go like this in the key of C:

Use C# instead of Db
*Use Eb instead of D#
Use F# instead of Gb
*Use G# instead of Ab
Use Bb instead of A#

The ones with the asterisk are the ones where this heuristic is probably most likely to be wrong. That is, in the key of C, guessing Bb instead of A# is likely to be right 90% of the time, but guessing G# instead of Ab is more 50/50. This is complicated by the fact that a C major key signature might really mean A minor. In A minor, it's no contest - G# wins for sure, in C major, it's more 50/50. And probably genre-dependent.