I love Aurifil for piecing because it's so very thin. Although I bought a huge spool of neutral polyester thread from Connecting Threads and piecing with that is really nice too.
For quilting, I'll use Aurifil if I'm doing stitch in the ditch, but if I'm doing a FMQ design or decorative stitching and I want the thread to show up, I go to my huge stash of Connecting Threads cotton thread and use that - it's thicker and shows up better, plus I have a lot more colors in that thread on hand to choose from. I use same thread in the bobbin as whatever I'm using on top.