I use the Copic BLENDING CARD X-Press It Paper. It is a good weight and I found it works well with Copic or ProMarkers. It does not bleed or feather at the edges of your image.
I used Memento's ink in Tuxedo Black or London Fog.
I tried Strathmore Smooth Bristol Paper 100lb., which worked good with Copics but not when I used the colorless blender- it caused the color to bleed around the edges. I think if the image had been bigger it would have worked better.
Other brands I have heard good things about, but I have not had any experience with:
PaperTrey Paper Basics - Stamper's Select White Cardstock
Gina K Pure Luxury White (80# & 120#)
Neenah Classic Crest Solar White
Here is a video on this that might be helpful:
Copic Paper Comparing - YouTube