You might find that the harmonic minor scale is a bit angular at the top of the scale to write smooth melodies. This is where the melodic minor scale comes in handy. It has a slightly different pattern of notes at the top of the scale which some composers have found easier to use to write melodies.
But, if you're composing, you're in the driving seat, you should use what sounds good to you! Mozart composed melodies with both the harmonic and melodic flavours of minor scale.