Of course there are wiser people on HF than me, so listen to them first. But my $.02 is this:
I use the all purpose coats & clark polyester, and have not had it do anything bad to me. It goes in easy, and I haven't seen it fray or break on anything I have made so far (stuff sacks, bugnet bottom entry hammocks, winter tarp). All of my stuff has had plenty of stress applied to it and seems to be holding up very well. I don't get too stressed about the thread.