Remember that if you're pressing with a cotton setting on your iron, serger thread is polyester. Use a polyester setting on your iron.
I prefer 100% cotton thread for working on 100% cotton fabric. It just makes sense to me. I buy 50 wt. Guterman on the big cone or 800 meter spool.
Polyester thread stretches, so I use it on stretchy fabrics and synthetic fabrics.
I do use Maxilock on my longarm and it works fine.
Serger thread is 2 threads twisted together. Regular sewing thread has a core with 2 or 3 threads wrapped around it.