Medium and Thin are the resins we recommend for smaller molds. They're also fine for molds a bit thicker like coasters and trays, just remember that they shouldn't be poured deeper than 1/4" at a time.
Also, think about what your end result will need to look like, the thicker the resin the more add-ins like glitter will suspend, whereas using Artist Resin Thin glitters will fall to the bottom of our mold.