Digital watercolour

Procreate

Good at very detailed drawings that build up gradually in textured layers. Use alpha lock for edge effects. Has the most control over brush shape. Bleeds have to be simulated through smudge tool and edge effects.

Adobe Sketch
Watercolour brush is the only one I would really use from the built-in toolset. Others can be imported from Photoshop CC. Has really nice bleed effects. Only flat and round brushes. Good for atmospheric effects. But difficult to get real subtlety.

Auryn Ink
Dedicated watercolour for more complex combined techniques.

TayasuibSketch
Can get nice Japanese watercolour effects with vector gradients.