I have not had the experience with the Tops paper as many of the reviewers have had. I am a third year engineering student and I have burned through thousands of pages of engineering paper of pretty much every brand there is and tops is my favorite.
Thickness- Its very thick compared to the other brands it "takes lead" well high friction minimal force required a 0.7mm lead and this paper are my favorite combination.
Line Clarity- The lines show through the front side of the paper so much better than any other brand I love it.
Margin Accuracy- The margins, lines, heading bars, are always identical throughout the sheets and look great they are the best dimensionally in my opinion as well.
The only problem I have with Tops is that the recycled material has tiny blemishes that look like "dots" made by a pencil maybe 2 or 3 of those on a sheet but after the paper starts to fill up with information you forget they are there...
Some notes about other brands- Ampad is absolute garbage they are the thinnest of all of them and the margins/header is always screwed up and varies throughout the pack, and the line visibility is weak. National is ok too thin for my taste I find that it rips easy especially under large amounts of erasing. My second choice for this paper is Roaring spring, you can't see the lines through the paper very well but this stuff gets the job done and can be had for the least amount of money in most cases.
Give this stuff a shot, I did and it's my new favorite.