When I see these "best cardstock" threads, or "best anything" threads, I feel compelled to be a little bit of a devil's advocate.
I always want anyone new to this hobby to know that there are as many opinions as there are products in the stamping/cardmaking world. Lots of the cardstock recommended here is very fine quality and they are great products to use if you can afford them.
I especially want to speak to those who may have limited funds to spend on this hobby. Do not feel if you can't afford the best quality that your cards cannot be lovely, or be appreciated. We all can aspire to better things, but sometimes the budget just doesn't cover it.
I use the inexpensive 110 lb cardstock that Sam's Club sells. My cards hold up well enough to go through the mail, be opened and appreciated, and stand up on a dresser or table.
I love making cards, and I love sending them to friends and family, who seem thrilled to get them. They may not be made with the finest materials, but they do come with the finest intentions and thoughts!
Okay, stepping off soapbox now.