I only use American Apparel t-shirts.  They are the smoothest and softest t-shirt you'll ever wear. Made of fine jersey, it has a durable, vintage feel. These classic-cut shirts are known for their premium quality, as well as ability to stand up to a washing machine (will keep size and color after many washings). The shirts are 100% fine jersey cotton.
UPDATE: Because of sourcing issues with the American Apparel Tshirts, I am using alternative made in the USA items as necessary.
Fine jersey
Slim fit
Double stitched
Made and printed in the USA, sweatshop-free