FulVal: with scan2x are better
I have checked it out a bit.
With scan2x you have for the lines:
Input (line 1)
Black
Input (line 2)
Black
Input (line 3)
Black
With scan3x, dosbox (and maybe others as well)
you have:
Input (line 1)
Black
Black
Input (line 2)
Black
Black
Thus the black parts are larger and thus it appears darker.
(scan3x (or any 3x scaler, means that we go from 1 input line, to 3 output lines)
I am pondering a bit on how it could be improved.
It would be easy to change it to
Input (line 1)
Input (line 1)
Black
Input (line 2)
Input (line 2)
Black
But then it might be too light.
Although it might be better to have
Input (line 1)
Black
Input(line 1)
Black
Input(line 2)
Black
Input (line 3)
Black
Input(line 3)
Which would be more difficult to code.
Or:
Input (line 1)
Input (line 1)
Black
Black
Input(line 2)
Input(line 2)
Black
Black
Input(line 3)
Input(line 4)
Black
Black
Which might be ever harder to add..
Ultimately it depends a bit on personal preference...
Might need to make some screenshots of the different cases and get some opinions (including yours) to see what is preferred.