I agree with what others said; in addition, an Aurifil stitched seam lies really flat when pressed.
When I order from Tristan (in Canada) several quilting friends join in - thereby distributing the shipping cost. Usually cost us no more than $5-6 a spool, including shipping. Be careful when ordering that your choice is the 50wt cotton.
Sometimes I just want one spool of a particular colour and I found a good USA source through Googling Aurifil.
Bottom Line (a Superior Threads product) is my bobbin choice always