Gina, my usual go-to paper for digital art is the semi-matte - almost matte but with a slight sheen that makes colors pop. Truly, it looks great an nearly every image. I like Somerset Velvet for more traditional-looking works, though it also looks great on everything. All the papers (and metal and acrylic prints) look great, if used for the right image.
Ordering some small prints in different finishes, using the same image for each, is a good way to sample them.
I'm a BIG fan of metallic paper, though it doesn't look great with every image; you have to use it a few times to get a feel for when it works and when it doesn't. The problem with using metallic is there's no way to demonstrate it in this POD marketplace. Printed metallic paper is a VERY different look than any other paper available here. There's really no way to convey that to potential buyers.
