Bruce Williams does a comparison in this video:
And AP’s comment explaining a bit more:
For this picture, the 3 tools make a pretty similar effect because it’s fairly neutral. If you try again with saturated colors, you will see how the RGB curve adds saturation in shadows and removes some in highlights. The tone curve tries to prevent that effect but turns the shadows blue-grey instead (one of the quirks of the Lab space, I suppose). Tone EQ does a simple exposure compensation, except it’s parametric, so it leaves colors alone. Also, it’s designed to complement filmic and that’s where the white/black points are set.
And Boris’ opinion on the matter: