Are we talking about hand sewing? Machine sewing? Piecing vs quilting?
I prefer a 60 to 100 wt for machine piecing. I do a lot of miniature and/or precision piecing, and I find that a strong, fine polyester thread gives me more accurate pieces. When your patches are only a quarter of an inch big, fine thread does make a difference.
For quilting, I prefer a 40 wt poly. Cotton gives off a lot of lint, and I've had the experience of a small piece of cotton shred or lint getting stuck somewhere in the thread path of my longarm and throwing the tension off.
Poly cutting through cotton is an old wives' tale and has been debunked.