I use Gina K Designs Pure Luxery cardstock-the 120lb. I've tried other papers but noting compares to Gina K's. Its thick and smooth yet still fits nicely into my printer (for digital stamps) Highly recommended!!!
I'm like CommaHolly..I'm easy to please with paper too. I but the 50 pack sheets of white cardstock when it's on sale at Joann's or Michaels 4 for $10 bucks! I hear all these stories about needing a specific brand of paper with copics.......not true!