Which banner material (substrate) should you choose:

Bottom line is, how you plan on using the banner, and for how long.
The biggest factor in long term durability is how the banner is hung. Using ALL grommets, reducing movement, and applying the banner with something behind it, will all improve the life and wear of your banner.

Here's a chart that should help you decide which substrate to use.

letterheightchart

13oz Matte and Gloss:

A Great all around substrate. Suitable for indoor or outdoor application. It is relatively durable and economical. The best choice for most applications.
Hung correctly this banner can even be used in windy locations.

18oz Herculite:

Very strong and very durable. Excellent choice for long term situations and for all outdoor situations. Carefully hanging your banner is key in keeping it for long periods of use.

Mesh:

Excellent choice for large spans and windy situations. Most commonly used in across-street applications. Care needs to be taken in designing on this substrate since this substrate lets more light through, and thus the design appears lighter. Stick with high-contrast, bold lettering and simple design when using mesh.
Again, hanging this banner type correctly will determine how long it can be used for.