Wow. Not to make your question seem small, but... wow. It's paper. As long as it's not pink or tangerine and doesn't smudge too bad, I really wouldn't worry about it.
Actually, I've heard some say that paper that's too heavy is a pain, because then carting the ms. around is cumbersome.
These are teeny little micro-managing questions. Use a good font, double space on decent paper. No sparkles, no curly fonts, no unicorn paper. See the thread on "proper manuscript formatting" and go from there.
Everything else... it won't make or break a submission. Worry about the writing. That's the most important thing.
