Superior Threads is what I like. Next on list is King Tut, then YLI.
I use 50 weight on top and bottom or 40 weight on top with 50 weight on bottom. It depends on the way
you want the quilt to look. Another good on is Invisafil, your quilt shop should be able to order it.
If you don't mind the lint Connecting Threads is another good thread, just remember to clean out the bobbin area
every time you change the bobbin!