User blog comment:Sprinklemist/Opinions on my art program, please./@comment-2021069-20110913232159

I'd say there's two major things to consider when you decide one over the other: style and difficulty. While the images you make in Paint.net and Paint Tool SAI are similar, each one has small differences in the style that your characters are drawn. PTS (which does sound like a disease XD) has thinner, smoother lines, but Paint.net allows thicker, more cartoonish lines. Another thing that might be worth noting is that the lines you use in Paint Tool SAI seem to be mostly curved, while in Paint.net they were mostly straight.

The other fact is difficulty: if one's much more of a pain than the other, then stick only to what you're comfortable using. Either way, your characters drawings are still amazing.