what is the best brush to create ceramic tile color effect?

I mean does it have to be a vector graphic?

As you could use Adobe Capture on your phone and use Patterns.  Then send what you create into Photoshop.  The cool thing is the image you create using your phone is seamless and then can be used to look like really cool tiles.

This is just an idea.

Exactly what is theprimary interest for you?

Is about how to draw the plants?

Or is it about reproducing an exact texture of those paint strokes? This would not be possible.

The pattern can be drawn using pattern brushes and symbols.

But you need to draw the elements that make up the patterns. For that I would try out width profiles. Then make those into brushes.

Here is a lengthy help article about brushes: https://helpx.adobe.com/uk/illustrator/using/brushes.html