There is so much personal preference in cardstock/paper used for copic colouring.
Well here is my personal opinion. I haven't tried a multitude of cardstock though, so my view is limited.
I started out with 110lb cardstock that I bought at Staples - the price is right for this, but I have to admit is bleeds quite a bit, as it is not a very tight weave to the paper. So, I would recommend it for when you are starting out for the price point, and you will be going through alot of paper to practice with. $17.74 for 250 sheets.
Then I moved to what Copic recommends for their markers - Xpress It cardstock, 110 lb, the price point of this the highest expect to pay $1 a sheet at your local scrapbook store. I like this paper, as it doesn't bleed very much, but, I do find that when I am colouring with multiple colours (layering) the cardstock tends to blotch and look shiny - not the look I'm going for.
I then contacted Gina K, and bought some of their 120 lb luxury cardstock, this is a very tight weaved paper and I have been extremely impressed. Very blendable, the ink sits on top just waiting to be blended. I have not found that it soaks through to the back like the other cardstocks. And at a cost of $6.96 for 25 sheets (plus shipping - to Canada is $10.90 unless you put in an order of $50 - and let Me know if you want to split on shipping I will gladly do it if you are in the Ottawa to Kingston corridor) They have the best paper I have tried.
Next up I would like to try the Neenah papers, but haven't secured purchasing any of that paper as of yet.
Onto inks now .... I find the best ink for stamping and colouring is the Momento ink (tuxedo black) but I have recently purchased the "rich cocoa" and haven't tried it. I also have used Ranger Distress Inks, and Stampin Up dye inks. All work well, but the Momento is the best. It doesn't smudge and it is a true black. If you are looking at printing out digitalis, I will tell you to only print on a LASER JET printer, do not, and I repeat NOT print on an ink jet ... it will smudge, you will get black shadows and your images will not be crisp. One other piece of advice - do not use heat embossing to set your images and try to colour with them.... this will ruin your marker tips .... learn from my mistake, my YG17 will never be the same!!
I hope this little ditty has helped you in dispelling some mystery and I would love to hear what your favorites are and why. Please leave me a comment. I might even have a couple of Copic Markers kicking around here to send to one lucky commentator for their trouble. Comments are always welcomed, but this give-away will close on April 21st 2012.
Remember I am teaching, in Cornwall, an Advanced Copic class on April 28th "Critters" will give you insight into how to colour all those furry little friends! Call Auntie Em's to reserve your spot - 613-938-4888