Okay, Ellie Poo might be the most interesting sounding paper I have ever heard about! I would definitely like to try that out.
I absolutely agree about printer paper. For water coloring it is horrid! It curls and the color doesn't spread at all. Used it several times for water coloring, because I just happened to starting to draw on it at work or where ever. Bad!
I use normal low priced water color paper ususally 250g for well, water coloring. I use this with water colors, pencils, inks and even copics. But beware, because it's not very good for the copic tips. But as I love to combine different media I use them anyways.
If I plan to color my pic mainly in copic I have a smoother sketch paper. That one is not explicitly meant for copics but works quite well. All of my action shots for the pinup calendar was done on that. I also bought a special (and quite expensive) copic paper pad, but I haven't used it so far.
I am actually still looking for the German equivalent for "vellum". The way Windrider describes it's advantages really makes me want to try it out! But I am still not sure what they call it here.