Here are the grey flannel swatches from my cloth hoard. I have them broken down into worsted and woolen.
At any given weight (10.5/11 oz, 14 oz, 17 oz), the woolen will feel "beefier" and more substantial. (Especially the woolens from Minnis) The worsteds feel finer and more delicate.
Here's a flannel suit from my personal collection. Make is Samuelsohn. I believe the cloth is a worsted. It's a 98% wool, 2% cashmere blend. Also seems be be in no more than 12 oz.
For my next flannel suit, I would prefer a heavier weight woolen. Probably a Minnis. The cloth on my Samuelsohn doesn't drape very well. You can see ripples forming in the back. I don't think a heavy weight woolen would do this.