The amount of printing resolution necessary for an image is dictated by the viewing distance. Most photography is meant to be viewed from 12 inches away or less. Therefore, I would suggest 1440 x 1440 dpi on an Epson, and 1200 x 1200 dpi on an HP, or Canon.
However, if you are using these printers to print a large banner, the viewing distance will usually be 10 feet away or more. Therefore, the required print resolution drops. In this case, I would print at 720 dpi with an Epson or 600 dpi on an HP or Canon.
I would also recommend that you print bidirectional for this type of job. One thing you should keep in mind is that a profile for this lower resolution and bi-directional printing should be generated to ensure accurate color reproduction.
