Hi there....just took a long arm course from a lady who has been quilting (long arm) for 12 years and she says that it is important to use good quality thread to piece a quilt(cotton) but use what ever works in your machine for the quilting....within reason....
Threads have come a long way and what you are looking for is the strenght of the thread....therefore polyester or cotton wrapped polyester will do a lovely job and looks nice as well...
If you use silk thread to do the binding(had sewn part) it will do nicely and goes throught material very easily...