I think you just have to keep trying until you find one you like.

The one I've been using for the past 15 years was given to me at a folk club in Standish, Lancs, and is a fairly heavy glass bottle neck with the end smoothed, and very slight curvature to fit my guitar neck. Infinitely better than the "Tyrozet" tubes I started with. I've always preferred glass to metal - probably something to do with the coefficient of friction.