For me I wasn't big into stamping so when I started I used Georgia Pacific paper that you can get at Wal-Mart or Sams. It's very inexpensive and works ok. It's completely fine if you're using any kind of colored pencil. The problem begins when you use markers. If you get to much moisture going it will begin to fuzz up and put a hole in your paper. That is not good when you've worked so hard on an image to have it ruined when you're almost done. So all of that to say if you're just starting out and you don't know if you'll be doing much it's fine to practice on and get going but I do have to warn you that you will be more frustrated using it than the papers that we're going to discuss next.
Neenah Smooth 80# cardstock is what I tried next. It's a little more expensive but the quality is worth it and really let's face it for 1/4 sheet of paper we're only talking pennies so take my advise and invest in better paper. It's acid free and solar white which means your colors stay bright and vivid. You'll thank yourself in the end. You can purchase Neenah at the following websites plus many more I'm sure-
I've colored on Papertrey Ink and I really like it as well.
Gina K is the heaviest of them all at 120#. I'm using it as of right now and I have to admit I'm having a bit of a learning curve with it. It was a very smooth almost wax like finish to it and if you use to much marker without letting it soak in it can smear. If you're cutting out any intricate images you have to remember it is quite thick and will be a little more difficult. I'm going to order the 80# next and test it. I have heard from others that use it and like it.
Prism Simply Smooth and Bazzil's new Coconut Cream cardstock can be found at many LSS and is said to be a good option but I've not tried it.
Now the question is what are some of the benefits of investing in quality cardstock.
#1 Money - For me I learned very quickly when I had so much bleeding that I cleaned up with my colorless blender and needed to buy a refill within the first month of getting into my copics. The small investment in quality paper is much cheaper than buying colorless blender.
#2 Time - I colored my images so much faster because the blending was almost effortless and I wasn't spending time cleaning up edges.
#3 Quality - My images look so much better. Like I said in the last point the blending is smoother and a better end looking product.
#4 If you want to color directly on a card and not mat it you can do this on the GinaK 120#. It does not bleed through to the back.
One other note about paper is one not to use. I love Stampin Up paper but it is said to have a coating that will ruin your copic markers so if you're coloring with copics I would warn not to use your SU paper.
Those are just a few of my plusses. I would love to hear about any other papers you've tried or experiences you've had with any of these papers. This is simply my .02 and not the Bible by any means. ;o)