I don’t use water brushes except in two places —
I keep them by the side of the bed (I am an insomniac, so also have a sketch pad
and travel watercolors) and when in the field.

Don’t forget, these brushes are not the greatest but still, I want:
a)  a brush that holds a point (if it is pointed)
and
b)  want the water to flow OUT not dirty watercolor paint to flow in (when doing a wash) and
c)  finally, how is it filled with water?  I know, some are designed to SQUEEZE
but frankly I’ve not found that effective because sometimes if there is a bit of paint left it gets squeezed into the water tube and I am fussy about clean palettes.
I want my yellow to be yellow!

PS: DO take a look at the comments below, because everyone’s experience
may be different!  It is a good point,and true, especially on items like this,
which are, in fact, rather cheap tools.  I welcome other viewpoints!

The line-up:

I’m not a Holbein Water Brush fan.  The good news is it holds the most water, and has an
easy-pour way of filling without losing a stopper-thangy (a highly technical term),
shown above.  BUT, The points don’t hold — so it is a stubby brush.
They also suck water up into the tank too easily which I don’t like.

 
I like Kuratake’s Yasutomo Niji Water Brush second best.
(There is the whole name confusion thing — Niji or Kuratake?
I don’t see Niji written anywhere but this is the brush!)
They have a flat which is nice.  However, the flat twisted almost immediately (see the twist?) and I don’t think that says much for the brush, plus it sucks dirty washes into it!.
They also don’t hold their point (not that any water brush is a great brush.)
I also don’t see much of a difference between the two sizes except one is shorter.
You can fill them with a suction motion but as I said, I don’t like that and so,
the little stopper-thangy gets removed.  I’ve lost one already.
I will buy another flat sometime, however.

For me, Pentel Aquash Water Brush is the winner. 

They hold their points better (these are not new brushes and look at those nice points!), have various sizes that are very different, and they are easy to fill —
no thangy to remove and LOSE in the field.
I have rarely had them suck a dirty wash back up into the water.  They are shaped
so they don’t easily roll!  When I see them on sale I buy several because
I also fill them (below) with liquid watercolors!

There are companies that make inked brushes.  My favorites, above, of
company-filled brushes are #3, #4, and #7; all the inks are waterproof.  In order of preference (and not a dog in the stack):

#3, my favorite, is not really a brush, the Platinum Japanese Art Pocket Brush Pen. It is not really a brush but a felt tip, and is wonderfully wet and lasts and is strong and waterproof and has cartridges. I’ve not had mine flatten yet, and I use a a lot.
I show it here because I always reach for it instead of my black brush pens.
What does that say about me, I don’t know!

#4, the Kuretake Zig Cartoonist Brush Pen No. 22 (Black), is okay, and can drop lots of black with a squeeze ( see that big blob?), but somehow I just don’t reach for it.   It doesn’t fit as comfortably in my hand, and I don’t feel like I have the control as I do with others.

#7, the Pentel Pocket Brush Pen for Calligraphy I like, but oddly, it is rather dry.
Maybe it is just mine.  Does have refills.  I may begin to love it when I pop a fresh refill in!

Sometimes I fill my Pentel water brushes with liquid watercolors, shown below and #1, #2, #5, and #6, above.  They can make teeny lines then drop lots of watercolor in a big blob and they have more control than the commercial pens.  And better color.  NOT waterproof, mine all use liquid watercolors and become custom color brush pens!
But once filled, I can’t imagine they can go back to being clean water brushes!

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