Your gonna get many opinions on this one, but I will give you mine.
Glass is versatile, can be loud, but also soft. More clear sounds.
Bead Blasted glass is similar to above, but I personally feel the sound is a little more deadened
Bronze Glass is more raspy to my ear than plain glass, but still able to be both loud and soft, and sounds more similar to crystal
Crystal is my favortite surface of any surface. It is in my book the most versatile, most realistic sounding surface for a call. It has a nasally rasp to it that is unfound in other calling surfaces, and in the right hands can make all calls from the hen vocabulary from roost pitting, clucks, barking yelps, feeding clucks, purrs, cackles, and even shrill kee kees. IF your looking for a good crystal surfaced call I will not reccamend any other calls other than either the Twisted Sister or the Crystal Mistress from David Halloran. You buy one of those and you will not go into the woods without it... ever.
Keep in mind the above is my opinions.
