Well, that depends on what you need the paper for. Brightness, opacity, and roughness are usually important characteristics. For instance, the brighter the paper, the better the color contrast. The more opaque the paper, the more it’s suited to duplex printing (printing on both sides). The smoother the paper, the easier it is to handle and write on. But all the characteristics really depend on how you plan to use the paper.
Grammage, for example, is another important aspect. The higher the grammage, the more professional your work looks (think of handing out a business card printed on a regular 75 g/m2 sheet of paper. It wouldn’t be the same, right?).
“…ALL THE CHARACTERISTICS REALLY DEPEND ON HOW YOU PLAN TO USE THE PAPER.”