Definitely acrylic for durability. Black acrylic looks every bit as nice as black vulcanite to me....and some pipes asthetically look better with colored stems, so I guess I prefer acrylic all around. The comfort factor is a moot point for me - I must have some super powerful jaws or razor sharp teeth or something, because I can even leave marks on acrylic stems with my teeth. Thus, all of my pipes* have some sort of protection on them - I used heat shrink tubing on one pipe, and I have softy bits on a couple (I chew through those too quickly), but my preference is to use clear vinyl tubing from the hardware store. It's by far the cheapest option, feels nice and firm, and is extremely durable compared to softy bits. The only downside is that it adds bulk, but I've gotten used to that and it doesn't bother me in the least. * that is, all of my pipes except my MM cobs with stock plastic stems. I don't mind chewing on those since they are only .50 cents each to replace. I keep a box of a dozen or so on hand.