i find that almost any cotton thread, 40 weight, long staple, will work well. some people like egyptian cotton only, or extra long staple, but i'm happy with 40-weight cotton long staple. i also use poly if that's the right color and i can't complain about that either. what i can't stand is the invisible thread for more reasons than i can list here.
in the bobbin, i use 40 also or 50. some people use thinner, but i don't like the way it interracts with the heavier top thread.
i think the king tut is too expensive and produces too much lint. i buy thread from superior and from bayside quilting, whoever has a sale.