All watercolor brushes and templates! The Watercolor Advanced Set has been an absolute favorite - make sure you check out some of the samples. There's also a Watercolor tutorial in the tutorials section which shows how to use the watercolor brushes.
These brushes work best on an iPad Pro with Apple Pencil, but will still work on an iPad Air with a different pressure sensitive stylus. The best way to ensure the brush will work with your iPad / stylus combination is to download and try the free brushes first :)