TC diaphragms, hands down! For distress or howling, they produce the most realistic sounds!!
Crit'r calls, Tweety, Tally-ho, Haydels, Lohman, & many custom calls have brought predators in for me over the years. They are all good calls, but the TC diaphragms consistently out perform them all by a large margin for me. I only wish I'd known about them sooner, when fur was still worth a little something.