A window painter's Brushes

Obviously 
you are going to need some paint brushes, 

but which ones are best for window painting?

This should be the first question you ask when you start thinking about getting your supplies.
window painter's brush set
A Window Painter's Paint Brushes

Which ones are best for you?

In The Essential Window Painting Guide you will learn the answers to this question and many more. I will share the ones I use then you can decide which ones work best for your style.

In this complete guide you will learn which brushes are the best for painting the base coat, which ones are used for lettering, and what specialty brushes you should have on hand for intriguing textures. You will also learn how to take care of them so they last you a long time.

These are the brushes I recommend and you can read more about them in The Essential Window Painting Guide.
The Lettering Quill
Lettering quills make lettering less of a difficult task. They hold a lot of paint and assist an artist in creating smooth lines and curves. They are a worthy investment and a valuable tool in a brush set. Use them for plain style wording or fancy calligraphy style script. A lettering brush will last years with the right care. Invest in a few of these fine brushes for the window painting kit. They make the difficult job of lettering so much easier.

Rinse out quill immediately after use. Reshape the top and lay flat to dry. Keep the quill handle side down to preserve the tip.
Blick Grey Quill, Set of 6

Blick Grey Quill, Set of 6

These traditional lettering brushes are crafted to stand up to the rigors of classroom use with ink and sign paint. They are effective for painting on glass and other smooth surfaces. - Set of 6
Liner Brushes
A good liner brush is an investment. The sharp, clean edges of a quality liner brush are unmatched with any tool for a window painting artist. The initial cost of a set of brushes is a bit pricey, but I guarantee they will last several years. Buying cheap brushes only adds cost to the set. Each year or after several uses, lesser quality brushes may need to be replaced or they fall apart a bit at a time leaving stray hairs in the paint. 
Kafka Design Short Stroke Brush, Short Stroke, Short Handle, Size 3 (1.6 mm x 36 mm)

Kafka Design Short Stroke Brush, Short Stroke, Short Handle, Size 3 (1.6 mm x 36 mm)

Designed by master pinstriping legend Steve Kafka, the Short Stroke is a special edition brush that contains a blend of natural and synthetic hair selected by Kafka himself. The brush features a gold-plated ferrule and a natural, stained handle.
Fan Brushes
The mighty fan brush. It builds clouds, trees, waves, and a variety of textures. The brush can be used for adding form and for blending. I use it for turkey feathers and other lovely touches. The textures created with this sweet brush is almost unlimited. 
Silver Brush Golden Natural Brushes, Fan, Short Handle, Size 2 (33 mm x 21 mm)

Silver Brush Golden Natural Brushes, Fan, Short Handle, Size 2 (33 mm x 21 mm)

Versatile and durable, these brushes duplicate the needle-sharp points and fine chisel edges of the best Red Sable. They contain a special blend of natural hair and Golden Taklon. Choose these brushes for exceptional color-holding and extra spring.