I use what I have. Some think that the poly thread can "cut" the cotton fabric, but I've read that is no longer true. I use what I have and have never had a problem.
If you are doing hand stitching, you may develop a personal preference for a particular type of thread so use whatever works for you, but don't be talked in buying more thread if what you have works for you.
My Viking is not particular, but some folks have machines that like certain brands.
Good luck