For piecing I generally use Precencia or Aurifil 50 wt.I recently purchased some Masterpiece from Superior Threads.
I use Coats and Clark Duel Duty to do hand binding because I think it is stronger. I use the Duel Duty for garment sewing. I like to use heavier weight cotton for machine quilting. But, I know a variety of thread is necessary for any sewing projects. I don't know about any of the rest of you but I know I spend a 'small fortune' on thread.