Use a resolution that matches the aspect ratio of your screen. SDL2 builds use a form of windowed fullscreen that scales the game resolution to your active screen resolution, and it uses pillarboxing/letterboxing to pad the sides out to avoid distortion. (By comparison, DD builds simply change the screen resolution to the resolution you're using, and most screens I've used - at least on laptops - will stretch and distort the screen by default. That's a horrendous default, by the way.)
One thing to note is the recommended "green" resolutions are all 16:10, and your screen is probably 16:9 in this day and age, so none of the resolutions that match your screen will match the recommended resolutions. But that's not as much of a problem in OpenGL since it just stretches everything anyway.