I use a wide variety of different threads depending on the effect I want. For micro-quilting I use Wonderfil's Invisifil 100wt. poly in top and bobbin most of the time, but I've also used Superior's 100 wt. silk (pricy but lovely) and Superior's 60 wt. Bottom Line which is poly.
When I am doing larger scale quilting I like Isacord 40 wt- also poly. I tend to use Superior's metallics and also their glitter and holographic thread for decorative accents- less breakage than other specialty threads.
I seldom use cotton for quilting since I don't like the amount of lint that even the high quality cottons produce. But if I want a particular effect or color and I don't have it in poly I am perfectly happy to use Superior's King Tut or aurifil 40 wt.
My Sweet Sixteen has done well with all the threads I've ever tried to use on it.
Rob