-File Spec-

1. What is the file spec for best Quality Printing?

1. Vector Format PDF, EPS, AI, CDR files (font outlined) in any size (graphic proportional to the size ordered)

2. if Raster (pixel based photo) image included in the file, JPG or PSD (Flattened) file would be the best
    JPG or PSD in 100% scale (full size output) at 100 dpi (Best)
    50% scale at 200dpi or higher (better)
    25% scale at 300dpi or higher (good)
    10% scale at 300dpi (minimum) 600-1200 dpi recommended

thumbnail size jpg, gif,, files would not print good quality banner
usually jpg or gif in under 100Kb in size

Again, size doesn't matter on vector format files
we can blow it up to any size at laser sharp image.