There was recently quite a discussion here regarding thread. You might try doing a search to read the different opinions. Also try the Superior Thread website. They have some videos that dispel some of the myths regarding threads.
My bottom line is use: 1) What works for you and what you are comfortable with 2) What you have on hand so you don't have to spend more $$ & 3)What your machine likes. Some people have machines that are particular. My Viking isn't too particular.
Good Luck!